ok, so my two best friends, Matt and Marcie, have been going out for over a year now, and today at my other friends sisters birthday, he went and kissed another girl several times, and not just any girl, she is a really good friend of both of ours and his ex from a long time ago. I am really good friends with all three of them, and i told Matt I wouldnt tell Marcie but that i thought he's a dumbass and he cant have both, but i am thinking that after what I saw him do, I am not required to keep that promise, I cant believe my friend would do that to his girlfriend while i sat a few feet away. So what should I do, 1) keep my promise to my friend of 8 years even though it makes me sick inside, or 2) tell Marcie what I saw him do and risk loosing 2 of my best friends.
ps: Marcie was not at the party.