I (27m) have been with my gf (27f) for 2 years. I found out from a drunk friend that when we were first dating casually, my gf was seeing another guy who was priority over me. The guy however ghosted her and so she made me priority after that. Now I find out she was seeing and sleeping with this guy casually while not really making much effort with me. However I really did like her in the few dates that we had so was happy to continue seeing her despite her being flaky (not aware at the time she was seeing someone else). In this time as we saw each other so infrequently, I was also seeing another girl but was not so sold on asking her to be my gf, so it was casual but we were sleeping with each other but i broke things off with her once I got with my now gf.. Now my gf apologized but admitted that what her friend had said was true and that she did come to find afterwards that i was the better guy. I told her it hurts but I can understand as we weren't really commited to each other at the time and I was seeing someone else too. I described the other girl in the scenario and she becomes angry at me. She claims i was "using" the other girl for s*x just because my gf wasn't putting out herself and that I must have done that as i felt entitled to s*x. How dare I use that girl the same way that it sounds like the other guy in this scenario "used" my gf. I told her that when dating casually like that these kind of scenarios happen if boundaries are not established - you can't really blame any party if that is the case. I don't really think either of us are at fault as no one lied and if anything, she was my first choice and I wasn't hers so I should have a right to be more mad at her imo. so AITAH here?