Do you ever really forget your ex?

I’m going to try to make my life story short; here we go! I was engaged abt 3 yrs ago to a man. Unfortunately things went left from both side; we started to fight a lot and insulted each other verbally & it was at the end a toxic relationship. We wanted different things in life, I wanted babies, het married and buy a house and he wasn’t into that yet. It was a serious relationship for almost 4 yrs and he was really committed to it and myself until it all crashed. It seems (Rumors) and suddenly happend to be true ay the end that he cheated on me with a co-worker in a job that I helped him find a couples of month before we broke up. Anyways we took different path and road. I am mow engaged to a wonderful really good man; I have a 7 chubby months old daughter; a house we my fiance and we are getting married next month. In other words I have moved on. It just that recently happened that my ex is expecting a baby with the girl he cheated on me with and it hit me like strike. I’m not hysterical crying or anything like that. Matter of fact I’m not crying or mad at all. It’s just the thought of (That would it be us if we wouldn’t broken up) im no going to say I miss him, but I do think abt him sometimes. It was a beautiful relationship at the beginning until he CHEATED on me of course. But thay doesn’t change the fact that he still cross my mind from time to time om what he is doing and what has happen to him. So my question is do we really get over exes?! Fo we really forget Relationships at all?! Am i wrong to even him crossing my mind?!