SUBREDDIT: r/relationship_advice
TITLE: My girlfriend wants to have lesbian sex to see how it is.
POST: We got drunk/high last night (which we often do as students) and my girlfriend was being a little flirty with a mutual friend of ours. No big surprise there, but later in the evening she straight up asked me if it was okay for her to have sex with her (our mutual friend). I was a little shellshocked, I mean, every guy's fantasy right, but only if they can watch... But now that I'm confronted by the idea for real, it seems like I'd be devaluing lesbian sex by saying it's okay for her to fuck other girls but not guys. And the flip side is, I don't know if I'm really against it, because she must really like the relationship or she'd just break up with me to go fuck chicks, but then again, telling her it's okay to cheat on me feels really unmasculine. I'm still drunk now and probably not in the best headspace to be writing about this, but it's keeping me up at 3:30 am.
TL;DR: 
My girlfriend got drunk and asked me if she could have sex with a girl. I don't know how to feel. Need advice.