We broke up

Me and my ex of two years broke up. I was very needy, and he didn’t have enough time for me or to put effort. I asked if we should break up and he said yes, so it was somewhat mutual. We had a beautiful two years together and he was my everything. We never had sex, and it’s been a while. It’s been a week and I’ve been letting myself cry it all out and be sad, we didn’t talk for all week but today we did and I apologized for all that I did wrong in the relationship. I want to have sex with a different ex, only because it’s what I wanna do and I’ve been with this person before so it’s more comfortable for me. This person meant a lot to me a long long time ago, but the feelings aren’t like that anymore. My worry is this. What if the boy I just broke up with comes back in a month, can he be mad about this? I’ve been sad and I’m on my self healing journey, but I just wanna do it not as an outlet or anything like that but just to do it. Am I wrong? Is he allowed to feel like that? Should I just do what I want?