There is nothing controversial about the chain, Promiscuity > Dating > Monogamy > Serial Monogamy (or serial coupling). In our committed relationships, however, we stress the differences between our monthly or yearly partners and those that receive only a few hours or days of our life. But both poles function in similar ways, what Badiou calls the One: a refusal to find Truth in difference, to commit to love, and to accede to love’s potential failures.
Now Badiou does not address the structural – or cultural – forms of contemporary romance. His is a philosophy without concrete examples (except for literature). In fact, if we take him at his word, employing the concept of ‘the scene of Two,’ then we may not see Badiou’s distance from the exemplary monogamist in Søren Kierkegaard’s Stages on Life’s Way. But where Kierkegaard’s married man and woman fold their lives into a One, an amorous fusion of lives – something Badiou wants us to eradicate -, Badiou claims love is an encounter between (or amongst as I’ll suggest) an immanent Two.
Let’s consider two ways of having love. Beauvoir describes inauthentic love as fusion: partners identifying with each other, or as each other. There is both a mysticism and a masochism at work here. On the one hand, an amorous ecstasy where Two become One in flesh and spirit. On the other, to annihilate oneself is also a masochistic desire in the sense of blending with the loved one at the expense of selfhood. Beauvoir sees this in the ‘woman in love,’ a woman so fueled by ecstatic union that she reduces herself to the man’s values and truths alone. There is nothing reciprocal between partners when Beauvoir writes:
The woman in love tries to see with his eyes; she reads the books he reads, prefers the pictures and the music he prefers; she is interested only in the landscapes she sees with him, in the ideas that come from him; she adopts his friendships, his enmities, his opinions; when she questions herself, it is his reply she tries to hear; she wants to have in her lungs the air he has already breathed; the fruits and flowers that do not come from his hands have no taste and no fragrance…. ‘I am Heathcliffe,’ says Catherine in Wuthering Heights; that is the cry of every woman in love; she is another incarnation of her loved one, his reflection, his double: she is he. (The Second Sex)
Although this union is described from the situation of the woman in love, its resonances cut across genders.
So there is the Two as One. There is also the One as seen or included as part of the Three. Kierkegaard’s married couple shed their individualities for the divine; Two become One under the banner of God. This is the ethical stage for Kierkegaard (and similarly applicable today with marriage substituted for ‘serious relationship’): in marriage, religiosity is the guarantor of two bodies uniting, a union of two which can then posit and hold one perspective on being-in-the-world. ‘[T]ogether they stand more firm than either of them alone.’ For Kierkegaard and his ethical marriage, woman is still subsumed under the divine guidance of man, but today we might suggest that the financial situation or child-rearing situation solicits of fusion of Two into One regardless of gender/sex.
The marriage certificate operates as One seen by Three as does the Facebook archive: husband and wife, in a relationship with, are both pronouncements by a mediator. In these ways of performing love, one body is amorously linked with a second, mediated by a third, and quickly returned to One, i.e., one perspective on the world. Where does promiscuity fit into this and what is its relationship to serial monogamy? Promiscuity is the One extended across a number of sexual encounters. Non-amorous sex posits and re-posits one ego contra the valuation and recognition of the other(s). In serial monogamy, similarly, one ego initially fused with another, breaks its bond to find itself a newer/better romantic relationship which best suits its narcissism (cf. Beauvoir on narcissism).
Badiou speaks to the lack of duration in love these days; we have lost the sense of surviving ‘catastrophic existence’ in our partnerships (In Praise of Love). Commitment to love is absent. He speaks at length about the absence of risk – love is always an adventure and a risk: a declaration of love may fail. Yet with Promiscuity > Serial Monogamy, both collapse love into a casual indulgence; for relationships in this chain, duration is not a matter of time, but the degree of fusion. With the former it is easy to pull oneself from the sexual encounter because fusion has not yet occurred; when turning from one monogamous relationship to the next, two individuals fused into one perspective cannot so easily wrest themselves apart. This is why, Beauvoir writes of the woman in love, ‘the absence of her lover is always torture’ (The Second Sex). A break-up is therefore extremely dangerous: half of the world goes missing, thus a substitute is immediately found. It is this kind of epistemological framework which has generated various neuroses today, such as the woman who cannot prepare a meal without her/a partner, and caused Hannah Black to frighteningly share herself with readers, ‘Pared back to the mode of survival, I realised I had become a couple better than I thought: I had become a couple so successfully that I had forgotten how to be a person.’This man had a similar experience after his divorce.
When the fusion of One is broken, the substitute partner in serial monogamy fills in the hole left by the absent partner. Thus, similar to promiscuity, no risk or commitment to love is present because the next partnership merely stands in for what has been lost – the process of fostering love, and its adventures, is foreclosed. This gap in existence is due, in part, to the myth of ‘true love,’ i.e., a ‘true’ feeling/attachment/whatever we believe ourselves capable of expressing prior to the process in which we may begin to express it. Put differently, the process is already standardized before another person is met. Indeed, this neglect of founding love together operates according to a fascist logic: love is ‘like this’ regardless of the other person’s desires, etc. This myth, which we all hold to varying degrees, pre-exists an individual with whom we may love (‘The Scene of Two’; IPL). Yet Badiou has said, ‘Just after the encounter you are seduced and you can not [sic] repeat the encounter. The initial encounter is lost. If you repeat the encounter, it is very artificial. Generally speaking, alas, it is impossible to repeat the encounter. If you do not do what was necessary from the encounter then you can not [sic] repeat the scene’ (The Subject of Change). Ultimately, serial monogamy shares promiscuity’s difficulties in founding an enduring love.
My contentious claim is that for Badiou’s philosophy of love promiscuity and serial monogamy are the same. Promiscuity is defined not merely as casual sex, but also as a lack of discrimination – this is what I’ve called the serial monogamist who fills in the gap left over by his/her departed lover with the first person to come along. I wrote about this at length in a review of Disney Frozen (2013). Thus an individual does not need to be promiscuous (in the participatory sense of casual sex) prior to dating, monogamy, and serial monogamy. The logic of promiscuity, as a lack of commitment, functions akin at the end of the chain. One partner is displaced and replaced. This is why our contemporary romances are of the off-and-on again variety; essentially one can be promiscuous in the sense of breaking up and getting back together indefinitely. We might go as far and say that promiscuity and serial monogamy are closely linked forms because two sexed bodies engage in non-amorous masturbation (‘What is Love?’). The failure of the chain, as I’ve outlined, is a failure to establish the scene of Two.
Two find love in a chance encounter; a declaration of love is performed to found a commitment, a fidelity to draw that encounter away from its randomness (IPL). Love does not pre-exist its process, Badiou argues (WL); it establishes the Truth of difference, the truth of Two unique subjectivities coming together to add another perspective to their being-in-the-world. For this reason, Badiou argues, love is a humanism and an ethics: ‘all love that accepts the challenge, commits to enduring, and embraces this experience of the world from the perspective of difference produces in its way a new truth about difference’ (IPL). The key term here is endure, and I saw exemplary instances of love enduring in the cinema of Tsai Ming-liang and in Michael Haneke’s Amour (2012). 
Many love stories in contemporary film try to replicate the promiscuity of serial monogamy: a tragic event (cheating or whatever), followed by a tragic break, then a new but less fulfilling love affair, and finally ending with the ‘healthy’ reunion of the initial pair. But if we take the tragic event not as a destruction of the One, but as a claim to the Truth of difference between the two persons involved, with this partnership founded by a commitment to stay with an in love through catastrophic existence, love will endure and perhaps be stronger for gaining an additional experience to integrate into the Two scene.
On the Truth of difference, consider the raw materials of heterosexual romance, i.e., two sexed bodies marked by their differences. The coming together of two sexed bodies necessarily posits difference (ST). The Two cannot be One at the most basic level. We can expand this example of difference to ontology, epistemology, and politics. The universal, for Badiou, is the Truth of this difference whereby we experience the world from two perspectives and not that of One (or, the paradox of this sort of philosophy, the universal Truth is that there are many truths): ‘The truth of the situation insofar as there exists two disjunct positions’ (WL). Love grants us such access through its intimacy, contagion, contact, affects, and longevity.
Given Badiou’s arguments and remarks, it seems that Two is numerically two simply for theoretical discussion. To escape the chain of Promiscuity > Serial Monogamy, and push Badiou’s thought to its social, cultural, ethical, and political goal, love should look more like: Love of One Individual > Love of Two Individuals > Love of Three Individuals > n … ‘One, Two, infinity’ (WL). This new chain does not foreclose the possibility of a one-partnered romantic relationship (although I suspect partners would not want monogamy if they adopted this philosophy of love); what is often foreclosed in contemporary monogamy is an openness to love as such.
Contemporary romance proceeds according to a serialization and substitution of loved individuals, thereby foreclosing love as Truth (and ethics). Indeed, Badiou has said that he still loves all those he had romances with (IPL). My argument is therefore not in opposition to monogamy but its recent incarnation that more closely resembles our practices of casual sex. For Badiou, against subjective and historical time and in favor of destiny (IPL), what matters is the commitment to love and Truth. This conclusion resonates with Deleuze’s philosophy of love in Anti-Oedipus much more than Badiou would perhaps be willing to grant (cf. The Clamor of Being), but I nevertheless believe it is the inevitable result of the philosopher’s hypotheses. In this new chain, what pre-exists the process of love is a commitment made to the Two scene and to ethics, then extended by lovers to a more firmly entrenched fidelity, and finally, to include Three, Four, and so on. What pre-exists love is not the will to true love or whatever, the anonymous person who fills the confabulated hole in existence. Love is a commitment to the Truth of difference, of disjunction and separation, of a multiplicity of vantage points.
 I’ll use the following definitions: ‘Monogamy was defined as reporting one sex partner over the course of the previous 12 months. Serial monogamy was defined as more than one sex partner over the past 12 months but with no overlap of first/ last sex dates of any other partners’ (Nield, Ph.D. dissertation, 2013). Although, what are called concurrent sexual relationships may also apply. The issue may be whether I’ve simply invented serial monogamy as the standard practice. Research suggests otherwise. It is the ‘normative pattern for sexual relationships among young people in Canada (Fisher & Boroditsky, 2000; Maticka-Tyndale, 1997)’ (Peterman, 2008).
 While clearly indebted to Badiou here, these arguments and claims had their initial developments after viewing three unrelated films: Derek Cianfrance’s Blue Valentine (2010), Disney’s Frozen (2014), and Joe Swanberg’s Kissing on the Mouth (2005).