Does this count as cheating? Should I just break up with this girl?

I was at a party with my girlfriend and she was playing beer pong with this guy. I was pretty drunk and just sitting down, and he made a bet that if she lost against him she would have to play the next round topless.

Next thing she loses - because she is bad - and ends up literally taking her tits out for everyone to see. Then the guy, presumably to try his luck, bet her that if she lost again she would have to suck his dick. My girlfriend turns to me then and says "Anon, I know I can win this time! What do you say?"

I thought she was joking, so I just casually replied "Yea, whatever."

Then she loses again, and this asshole says something like "Hey, a bet's a bet." and my girlfriend responds with some bullshit like "Well
I am a woman of my word.". Within the space of fifteen seconds she's then literally on her knees, topless, sucking this guys dick. There was nothing I could do about it.

Because of that I just turned away and pretended to see nothing / try to not look like some beta faggot. Then after a couple of minutes I hear him saying "Go, show him. Let him see" and my girlfriend taps me on the shoulder, opens her mouth full of him cum, then closes it again and swallows in front of me.

What the fuck just happened!?!?!?!?