I have been dating my girlfriend for about a year and a half when I had to go on this big corporate retreat thing that would last for 2 weeks. Due to a mix up, I was put in a hotel room with a female co-worker, even thought it's wasn't suppose to coed. Anyway, Due to circumstances we were stuck together and while we didn't know eachother before the retreat, we quickly bonded over our many shares hobbies over the first week. I never told her about my girlfriend (I lied about it, which is I guess a detail that is signifcant) and long story short we went out for drinks and ended up sleeping together that night. For the rest of the retreat, I basically was in a relationship with the coworker, taking her out a lot and basically treating her how I would treat my girlfriend, although neither of us said we were a couple. So end of the two weeks, co-worker goes back to other side of the country, and I'm back home with my girlfriend, acting as though nothing happend. Should I tell my girlfriend about it? Should I keep in touch with the girl I cheated with (we have texted back and forth a couple times, but we both agree we don't want to do long distance.) The guilty is driving me crazy, but I don't want to lose my girlfriend., she is amazing. What do I do?