Should i feel so guilty?

when i met my bf he was married, he told me that he wasn't at first. i found out and he told me the truth. He left her for me. He never cheated prior to me and he was in a 10 year relationship at the time. He always asked questions about past bfs and i never fully disclosed details about all my relationships because i felt that he would be judge mental (nothing that bad).He also confessed about 3 months ago to me that at the very very beginning of our relationship (after he slept with me) that he slept with his ex one last time. I ended up leaving our apt about a month ago after an argument (after he went to his moms n stayed for 2 days without a word), i thought that he had left and was just waiting for me to leave so he could come get his things. so i moved out. I was very distraught and hurt, I went out to a club the next night and ran into a guy from high school and I slept with him. I felt guilty immediately. my bf wrote me an email telling me that he did not leave me and he loved me and etc.... so i went home. I confessed what I had done to him the day i went back, i felt massive guilt. I also told him everything about my relationships from the past that he wanted to know. I laid everything out and was honest. He was very angry...we made up said we were going to start over. I still feel guilty. he said i was cheater, throws it in my face and then apologizes. But he does not consider sleeping with his ex after me cheating because we argue about when our relationship was "official". I thought it was, he told her about me and he was planning on being with me.he considers me a cheater but not himself? I feel horrible about what i did because I am not that type of person normally, i dint know why I did it, I got nothing out of it, I didn't even enjoy it. Ive always felt resentment for him not admitting that what he did was not cheating on me and making me feel wrong for thinking that way and then calling me a cheater when I though we were broke up! Yes, sleeping with another guy 24 hours after I move out of our house is stupid and morally wrong and just cause I didn't say "i break up with you" to him, im a cheater. I would think that moving out would mean that we were. I did email him right after i was with this guy and told him i want to come home. WTH should i feel guilty or am i being bullied into thinking something that isn't correct?? HELP!