Boyfriend troubles? Anyone willing to help the most confused girl in the world right now?

Okay so this may be slightly confusing seeing as the people I'm talking about have the same names. But we'll call them A and B to make things easier, yes?
A = my boyfriend.
B = his like best friend [Anna's boyfriend]

So basically, this morning my friend tells me this:
A and B are going to the Isle of Wight festival today until Sunday. B told Anna that A suggested they make a pact, that would mean they could have sex or do anything with any girl at this festival and they wouldn't tell anyone. So B told Anna, as she is his girlfriend after all.

So this is just great right? I hear that my boyfriend is basically planning to cheat on me this weekend. Isn't it just great that I've already put up with a lot of his shit anyway?

This past week I have been in one of those moods where every teeny thing about him is just annoying me and I was just thinking about ending it anyway.
But when I found this out it hurt a lot more than I thought it would. I got that horrible sinking feeling in my stomach and the whole day has just been rubbish.

I don't know what to do guys. Somebody help me? please?

Fock.