Still having dream about my ex...

I’ve been married for 10 years. We are fairly happy and have 3 kids. However, I annoying can’t stop dreaming about my ex boyfriend from 15 years ago (it was very serious and we were together for several years). I don’t have feelings for him anymore, I don’t talk to him or want to be with him, I’m glad I’m not with him and married to by husband instead. Why do I dream about him? We did have amazing sex but a horrible relationship that I thank God ended when it did.

I don’t dream about him often but why the hell is he still in my dreams 15 years later. It haunts me.