Pretty sure girlfriend cheated, or at least attempted to cheat

I am pretty convinced my girlfriend of 2 years has cheated on me or at the very least attempted to cheat on me with one of her guy mates when she was drunk. She knew him well before she ever met me. I was working that night. I came across a message that she had sent him (yes i know - poor) which reads as follows;

"Hello, I understand I was bring a bit of a creep last night, I'd like to put a big curtain over it. I can't even remember...I hate not remembering, I usually remember most things when I've had a drink. But anyway, I apologise for the whole conversation."

The guy friend replied...

"Don't worry about it bro"

I have met the guy before and he seems like a pretty decent guy. I could have had a beer with him.

Prior to this, I knew my girlfriend was crazy about me but in my opinion when someone is drunk anything could happen.

Now, i don't know what to do. I don't want to bring the matter up with her as it would probably cause drama. But I can't go on with this suspicion.

Now now, your over reacting. I don't care how drunk a person gets, when/if that excuse is used or accepted I think, lame, lame, lame. I don't think 'anything' can happen when one is drunk.

Your partner may have been loaded and hung out with her mate and maybe she said some stupid stuff, that is all.
If you can't shake the bad feelings though, invite the guy over for dinner and see how they react around each other as that would tell you more.
but in my humble opinion, your lady did not cheat.

Um, if I were you, I would bring it up to her pronto! It sounds to me like your girlfriend not only can't handle her liquor, but has the wandering eye for sure. As a girl, I can tell you that when she messaged him the next day (or whenever it was), apologizing to him, she was trying to reignite a conversation with him to get a better feel for how he felt about things. He seems like a good guy, calling her "bro", as if to say, "We're JUST FRIENDS...take the hint!"

Maybe ask him what's going on. Dudes are more apt to be honest with one another...especially when their girlfriend is being sneaky and they know about it. Obviously, you can't really trust her, so I would almost not even bother asking her about it at all. She'll try to turn the tables on you and ask, "Why were you going through my phone??"

YOU: "Because obviously I can't trust you!!" Haha

Good god, I hope you find out the truth and bail on this chick! You deserve way better.

Thanks for the comments guys. From reading it I don't think she has cheated but I can't eliminate that she didn't attempt to as that message sounds a bit suspicious to me, almost as if he has had to reject her. Maybe overreacting but I can only bring it up with her if there is any evidence and that message doesn't confirm it which is really doing my head in. For now I will just need to see how it goes I think.