Couples, Sexual Health, and Group Sexual Encounters

The sexual behavior of sexual minority men in relationships is the subject of a lot of research. This is due, in part, to the prevalence of HIV in this population. Studies have examined sexual agreements and misunderstandings, commitment and sexual decision making, as well as drug use and sexual risk taking. A curious detail is evident in these studies. Condomless sex with a relationship partner and condomless sex with outside partners (any partner other than the primary relationship partner) tend to be positively correlated with one another, regardless of how these behaviors are assessed.

• Those who have condomless sex with outside partners (at least once in the past 30 days) are more likely to have condomless sex with their relationship partner (Starks et al., 2015).
• Those who have condomless sex with outside partners more often also have condomless sex with their relationship partner (Starks et al., 2021).
• One study even observed that condomless sex with outside partners was significantly more likely on the days that condomless sex with a relationship partner also occurs (Starks et al., 2021).

This correspondence has health implications. If either relationship partner contracts HIV or another STI during sex with an outside partner, they could subsequently expose the other partner during sex together. Estimates suggest that between one-third and two-thirds of new HIV infections among sexual minority men is transmitted sexually between relationship partners (Goodreau et al., 2012; Sullivan et al., 2009).

Our recent study (Starks et al., 2025), published in The Journal of Sex Research, examined this association in more detail. Group sexual encounters are common among sexual minority men (Goedel & Duncan, 2018). Some couples form specific rules (Dellucci et al., 2025; Grov et al., 2014) or agreements (Cain & Starks, 2024) that permit sex with other partners only when both relationship partners are present. We considered a novel question.

What if relationship and casual partner sex co-occur because the couple is having sex with a third person or attending a group sex event together?

Unfortunately, very few studies have collected or analyzed data in ways that would allow them to observe this.

Study design

Our study utilized data from 184 cisgender sexual minority men aged 18 to 35. Everyone was HIV negative and 56% had a current PrEP prescription. Everyone was in a relationship with an adult cisgender man and had a non-monogamous sexual agreement, meaning sex with an outside partner (any partner other than their primary relationship partner) was in some way permitted.

Participants reported their sexual behavior in a time-line follow-back interview (Sobell & Sobell, 1996). They filled in a calendar of the past 30 days by indicating days on which they had sex. For each sexual encounter, participants reported: partner-type (relationship or outside), whether a condom was used, and whether sex with their relationship partner occurred during group sex or one-on-one.

Analyses accounted for drug use, PrEP uptake, relationship quality, and demographic characteristics. Findings showed a clear pattern.

• When participants had condomless sex with their relationship partners during group sex, they were 495 times more likely to have condomless sex with an outside partner as part of that group sex.
• On days participants had condomless sex with their relationship partner one-on-one, they were 66% less likely to have condomless sex with an outside partner.

Implications

When a couple decides to have sex with others together, the potential for relationship partners to be simultaneously exposed to HIV or another STI amplifies the potential for transmission between them. Consider two fictional couples.

Evan and William recently had sex with a mutual friend together. Unbeknownst to either of them, they were both exposed to Chlamydia during that encounter. Evan took DoxyPEP (an antibiotic taken after sex) to prevent infection. William forgot to take DoxyPEP. Even though he developed an infection, William did not have noticeable symptoms. So he did not worry about getting tested or treated. Evan could now be exposed to Chlamydia again through sex with William.

Juan and Kit attended a sex party while on vacation together. Both were HIV negative and neither of them was taking pre-exposure prophylaxis (PrEP, an antiviral taken before sex) to prevent HIV at the time. Juan contracted HIV at that party. Three months later, Kit completed an at-home HIV test and received a negative result. Both Kit and Juan assumed that Juan must also be HIV negative because they “basically do all the same things.” This error in their logic increases the likelihood that Kit contracts HIV through sex with Juan. It also delays Juan’s diagnosis and treatment.

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Staying healthy together

When having sex with other people, relationship partners can address some of their shared risk by coordinating prevention and treatment decision-making. A few principles might help.

If either relationship partner has sex with someone else, they should assess their own risk for HIV or other STIs. They should also assess the risk that they could expose their partner to infection during sex.

• Are they using PrEP? Is their partner living with HIV? If not, does their partner use PrEP?
• Have they taken DoxyPEP for STIs or PEP for HIV infection since the encounter? Could their partner access those prevention options?
• Have they been tested for HIV or other STIs since the encounter? Has enough time passed for those tests to accurately reflect their exposure?

Relationship partners should assess the importance of sharing HIV and STI test results with one another.

• If one partner learns they have HIV or another STI, it might be important for the other partner to be tested as well. The couple may need to consider strategies to prevent transmission within their relationship.
• Beware of assuming relationship partners will automatically have the same test result. The best way to find that out is for both of them to get tested.

See here for more on joint-coping and the importance of partners working together to prevent HIV infection!