Why Can't I Get Over My Ex

My ex and I started out As BFFs for about 6 months then we decided to try out a relationship it was cool at first until we started having sex then I realized how controlling he was. After a rocky year and a half we called it a quits . Months after I found out he was being unfaithful the whole time which crushed my heart even more. Even through all of this , to this day (nearly 2 years later) I still think about him daily, I still dream about him, and I still question if I gave up on us to quickly... Smh I can't understand why I haven't moved on. Since then I've been in another relationship but that doesn't matter , he's still all I think about 😔😔