When people break up is this normal?

So, I may have went through a bit of a "slutty faze". I was with this guy for 1.5 years and I found out her was cheating on me for a year of it, obviously we broke up cuz of it. Well than about a week later I started seeing this other guy (who was also a pos) and I cheated on him with my ex, I mean, not just once. I was really attached to the sex with him :( Than I stopped doing that and became faithful to the "new" guy and things were good to us up until I hooked up with his best friend. I broke up with him and started dating his friend. We're still together as of now but now for some reason I can't stop thinking about sleeping with my last ex. What is wrong with me?!