[Serious] People who cheated on their SO, why did you do it?

Sorry for the length:

Several months before I met my ex J I was friends with this guy named M. We hit it off and hung out many times and talked a lot. Had a thing for each other but it never went anywhere because we were too shy. Met J and hit it off with him and after dating for a short time agreed to be his girlfriend even though I wasn't ready. He was immature, I was 25 and he was 20, had a great heart, fun to hang out with and treated me well, but he wasn't the smartest, made foolish decisons, was childish and ended up cheating on me. I left him and found out M had left the girl he had been dating too. We confided in each other and reconnected, but I ended up forgiving my ex, and stopped talking to M. My relationship started failing as there was no trust and I wasn't happy with him anymore. We started arguing a lot and one day I couldn't take it anymore; I ignored him and hung out with M and our closest mutual friends. We were drinking and the sexual tension could've been cut with a knife. I said "fuck it, I'm leaving J anyway" and proceeded to hook up with M.

I was angry and wanted out of my relationship since I wasn't happy. I thought M and I would be perfect for each other, but after we were done hooking up I immediately left. Apparently I hurt M's feelings as he wanted something more but I was so disgusted by myself and with him our friendship basically ended. I fessed up to J and he lost it. After a messy 2 weeks of trying to fix things I found out he'd already been talking to someone, and knowing his past of cheating I gave up and let him be. Was an awful way to end the relationship, but it was for the best; he was an absolute idiot and I ended up finding the man of my dreams and soul mate about a month or so later. My ex ended up dating the girl he was talking to during the two weeks we were trying to fix things, shocker, but continued texting me, talking to me at the bar, trying to hang out, and once at our mutual friends house grabbed me and kissed me.

I don't regret what I did to him, he was a shit person, but I regret not holding to my beliefs and morals in a moment of weakness.

/r/AskReddit Thread