My (28m) girlfriend (27f) kissed our roommate (25f) when drunk after I explicitly asked her not to

I really need some advice on how to tackle this with my partner. We were out at a club last night with a few friends, we’d been drinking all day and everyone was quite wasted.

Late in the night my gf invited our roommate to join us- no problem with me, I don’t dislike her. She’s not the best roommate, has been late on rent a few times, can’t hold down a job, a bit lazy but she’s definitely not the worst I’ve lived with.

She was absolutely trashed when she got there and was struggling to stand up right, my gf being a good friend was spending quite a bit of time with her, making sure she was ok, getting her water and the usual friend-is-too-drunk care.

I noticed the two of them dancing on the other side of the booth and our roommate was getting pretty handsy. Shes bisexual (recently discovered, was previously gay) and I could tell based on the actions and body language it wasn’t just dancing – she was very clearly putting moves on my gf.

Some important context here: my gf and I are monogamous but have played with other women before, threesomes etc. but neither of us have any interest in our roommate.

I’ve always trusted her and I thought hey, not loving what I’m seeing, I went over to them and as soon as I went over and grabbed my gf our roommate just dipped very suddenly, as if she was caught doing something she shouldn’t have been doing. I told my gf hey, don’t hook up with her please (I’m fine with her kissing other girls but roommate is a no-go, too much drama can come from it). She acknowledged it but was a bit confused, tbh she can be quite naive when it comes to reading other peoples intentions especially when drunk. She’s also a self-proclaimed attention-seeker, this has been a pain point in the past as our sex life hasn’t been great for a long while.

Anyway, after talking to her I went back over to some other friends and noticed the roommate reappear, they got straight back to it. I was looking at my gf and very clearly mouthed “no” and shook my head. She kept going, they kissed.

I walked out of the booth for a bit to have a smoke, came back and the two of them are in the booth on the couch all over each other. I came and sat next to my gf and told her to please stop. She seemed surprised, like she didn’t remember the conversation we had 5 minutes earlier. I set a very clear boundary saying I’m not ok with this and to make sure it doesn’t happen again. Our roommate is sitting on the other side looking quite anxious and had totally disengaged from what they were doing when I came over. Girlfriend again acknowledged what I said and said she’d stop. All good, miscommunication, it was loud, everyone’s drunk. I get it we all do stupid stuff when we’re drunk.

Not 10 minutes later I go back over and they’re still on the couch, she waves me away in a shoo motion repeatedly and tells me to go away. They kissed again. At this point I’m pretty upset but keeping a cool head for the sake of not publicly starting drama in front of our friends.

When we get a few minutes alone I tell her in no uncertain terms she’s crossed a big boundary and what she’s doing is very dumb, she’s our housemate, messy, stop. I tell her I’m pretty hurt by her actions and the way she’s disregarded me and my feelings. She tells me she’s just “looking after her” because she’s drunk. I tell her she can do that without getting physical with her and that she needs to stop asap. She barely seems to care but does stop after this.

I go down to the dance floor to hang with some friends and the two of them come down and seem surprised to see me and don’t dance with me, moving away from me and our friends.

We all get home that night and I ask our roommate to leave us to talk in private which she does, I tell her the way she acted really hurt me. She immediately spins it around, says I’m threatened because she’s a lesbian, that I’m being insecure, that she’s participated in all of these threesomes etc “for me” even though she’s wanted to do it just as much. Things escalate a bit and I think we had the worst fight of our 1.5 year relationship. I tell her I just want to feel heard and acknowledged, she completely refuses, starts saying she doesn’t remember any of these things happening (right after admitting these things happened).

She’s now sticking to the “I don’t remember” story and I told her this is a huge breach of trust and I sincerely tell her this could break our relationship with the way she’s acted and disrespected me.

That was the only thing that made her apologise, and even then she tells me I’m manipulating her and that none of these things happened.

It’s the next morning and I’m still very upset, I don’t know how to navigate this, she’s a great partner and we’ve never had an issue like this. Our communication and respect of boundaries has always been good, we’re very compatible in every way I could imagine with the exception of the sub-par sex life.

I don’t want to end it but I’m seriously considering it because I feel so hurt by this and don’t know how we come out of this. I plan to talk to her again today but I really need some pointers on how to approach that conversation.

Any help would be amazing because I’m struggling to think of how to fix this with her, does anyone have any pointers?

TLDR: gf kissed roommate at a club when we were all drunk repeatedly after I asked her not to. We had a massive fight about it with her denying it happened and I don’t know how to talk to her about it