The last time I posted here in regards to my gf wanting to attend a birthday party where there would be previous fuck buddies present, everybody told me she was looking to fuck Chad and I should cut my losses and move on. Well, I took some of the less harsher advice that was given and she did not attend said party after giving her a choice, and she ended up coming to my place where she fucked and sucked me all night.

I’m in a similar situation here where it’s a friend of hers surprise birthday party, and I am invited. There will be 1 guy she fucked before me at this party, and she made me aware beforehand. Truthfully I don’t want to go at all, but if I don’t go, it’s basically preventing her from supporting her friends birthday party because she knows I don’t date girls who party without their BF’s. I’m 100% a redpilled guy, but even I know it’s fucked up to prevent your girlfriend from going to a birthday party when you were invited just because you don’t want to go yourself. If I go that route, this will be the second birthday party my gf didn’t attend due to my boundary. So I’ve decided to accept the invite and attend.

With that said, how do I conduct myself around this guy? They were genuine friends with a few drunken fucks along their relationship, and she never speaks or communicates with him since being with me except for in passing (it’s a small college). In fact, my gf was a virgin when they were friends (no, he didn’t take her virginity lol) and after years into the friendship they became fuck buddies.

I’m just trying to gather some general tips because it’s inevitable that they will run into each other. I’m not worried about anything sketchy going on - the dude has his own girlfriend, but where do I draw the line as to what flat out disrespect would be? Like, they get aquatinted or whatever, but if they continue to talk to each other should I just dip out and soft next her? Because I know very little people at this party and I feel it will be difficult to maintain frame, so I’m even contemplating making another plan and ditching last minute. But if I do that, it’s still a lose lose situation because either A). GF goes to party alone, boundary is broken or “exception” is given (I know, big no no), or B). GF doesn’t go, stays home alone, grows resentment and the LTR is tainted.

How do I manage this from a frame perspective?