First of all, let me apologize for not being here to reply--for years! I had a lot of personal family medical situations to deal with and I've only just now returned to BOL. If you're still here, please accept my apologies and also my thanks for your interest, time and kind support.
As for dreaming about your ex still, there's nothing to fear until your dreams upset you. People in our past, especially those we once loved, become part of our emotional fabric. We can't just cut them out of our existence because we are shaped by every encounter with others.
If you should wake up feeling anxious about your ex dream, you might want to see if there are unresolved issues in your mind regarding this person. Otherwise, you can simply just acknowledge your shared experiences with him and move on. He's in your memory bank and that is all.
I had dreams about an ex where he was chasing after me and I was terrified. In our waking lives, he did stalk me for a while but eventually moved on. The dreams subsided after that because I was no longer fearful of him.
I hope your dreams are not upsetting.