My ex wanted to stop sleeping together when he started dating someone and he changed his mind why?

I dated a wonderful man when I was a teenager, and his family moved him away after about a year of dating, I moved too and we lost touch, almost 6 years later we reconnected, but I had already gotten married and moved on, we start sleeping together and he begs me to leave my husband, I want to, but im afraid on the instability, what if we don't work out, what if things are different... We spend the next 4 years going back and forth from trying to make it work. This year we said we wanted to make the relationship work, but I told him that if he met and clicked with someone, we could be platonic. He did meet someone and they started dating, we slept together once while they were dating and he felt bad and cut it off again. We hadn't spoke for a few weeks, I needed space, and I wanted to give him the space to pursue his relationship. After about a month, he starts texting me and calling me telling me he misses me. I told him how he hurt me and how I'd be wanted to get back together, that if he hurt me again I was done, and asked him if he would get upset about cheating again and blow me off. He said he made a mistake and wouldn't leave again. My question is why did he change his mind, he said that he missed me, and couldn't stand the silence anymore even.