What should I do about this problem with this guy?

Hello, everyone. There was a guy I was seeing for a very brief time a few months ago, but I broke up with him because I was unhappy in the relationship. He was controlling, convinced he was more intelligent than everyone else, and very mocking. When I ended things, I felt relieved that I no longer had to deal with him and got over him real quick. However, recently, my mind keeps returning to him and how angry he had made me feel at times. I even had a dream with him in it; he kept stalking me, and there was no way to escape. Have any of you ever experienced anything like this? Why are all these bitter feelings rising up now? Your help would be appreciated.