I have several dreams about my Ex a year.
I think a lot of mine is linked to guilt though.
He wasn't perfect [undiagnosed MH issues] but he adored the bones of me and I never really felt the same way.
We were together for 5 years, lived together but I was never truly happy. I stayed as it was the "easier" thing to do. Gradually it ate away at me though and I became increasingly unhappy.
It all came to ahead when uncharacteristically we had a massive argument, it got very ugly not violent but I was pretty shaken up so I walked out.
Ex expected that we'd patch things up, as I say it wasn't a regular thing, but the moment I left I felt free and I never went back.
I wasn't completely honest with him to begin with, I maintained a friendship for a few months as I didn't want to cause more angst but eventually I had to take a deep breath and tell him that a) we'd never reconcile and b) I'd never been madly in love with him and c) I had met someone else (my current DP, who I met a few months after leaving Ex)
I felt free leaving my ex but the guilt I carry for the way I hurt him manifests in my subconscious and I dream of him still almost a decade on.