There are two futre states of the world, depending on your course of action. If you tell your gf, you enter state 1. Otherwise, you are in state2. State1: You tell your gf. She is heartbroken. She breaks up with you OR she can never completely trust you again. You get rid of your guilty conscience, but you hurt your gf, and worse, you could end up losing her and she could never trust you completely. State 2: You stay mum. Your girlfried never finds out (unless the friend tells her). She is oblivious to the fact. You have a nagging feeling, but like most feelings it will weaken with time. For your girlfriend - ignorance is bliss. You keep your girlfriend, and she trusts you. The bottom line: You cheated on your girlfriend, so you deserve to be kicked in the nuts. However, telling your girlfriend will create more hurt and feeling. Just cos you let that thing off your mind does not mean that you will feel better. Your girlfriend probably deserves someone better, but since you came here for advice I guess we should help you out. Note: the girls responding are all putting themselves in the shoes of your girlfriend. And they all say that you should spill the beans. Of course they would say that. hehe