The one constant that I've noticed is that your girlfriend brings these accusations to you, you ask your friends about them, and they have no idea what you're talking about. Is it possible your girlfriend is making this up? The few times I've had enough to drink that I actually got sick in a bar I don't remember the whole night. Is it possible that you did kiss your friend? Maybe you're bi, you had no qualms jumping into bed with an openly gay man.