I (22m) saw this girl (23, call her Gal) for a total of 5 weeks.  I could tell by week 2 it wasn't going to work, but being inexperienced and from a broken home I wanted to try my best to make the relationship work.  At the end of week 5 my (friend 1) was celebrating her birthday by drinking downtown friday night.  I invited Gal, but she would only come if I didn't drink.  That would have totally killed (friend 1)'s vibe so we just set up a date for that sunday and Gal didn't come drinking, no hard feelings, I think. 

Details real quick:
By the beginning of week 5 I had a strong feeling we needed to break up.  Not only did we not have much in common,  she was constantly mad at me because of misunderstanding what I was saying.   I'll be honest my sarcasm is a little dry sometimes but it ended up me weighing my words too frequently for me to be myself around her.

Back to the end of week 5, the night we're going to go out drinking.  We're pre gaming at (friend 2)'s place and as I'm getting an uber I get a passive aggressive text from Gal about having not talked to her at all that day.  I hadn't made much of an effort to talk to her that week,  and the combination of considering breaking up and knowing I was going to see her that Sunday made me not really think about it. 

Anyway that text was it for me,  I knew reading it that I was intoxicated and not going to try anything rash, but was 100% breaking up with her the following day (saturday). I diffused the situation  and told her I was a little drunk and I'd talk to her tomorrow.

That night we all got very drunk.  At the end (friend 2), and two strangers, a guy and a girl (friends not dating),  came back to my apartment to drink after the bars closed.  (Friend 2) was totally set the whole night to get this girl to sleep with me.  Me, drunk as fuck with 0 game, thought this was a great idea.  I can tell pretty quick she's not interested so I drop it and just enjoy destroying these people at beer pong.

As we finish up the last game of whatever we were doing I go around for high fives.  This girl comes back with a kiss.  It was fast,  but it sobered me up real quick.  Nothing else happened and everyone left ~30 minutes later but I felt awful. 

The next morning I broke up with Gal over the phone,  totally hungover, and I didn't say anything about the night prior.  My concern here is cheating.   My friends have said it doesn't matter because nothing happened,  but I don't think I would have stopped her had it continued, and I don't know how to feel about that.