What to do when your ex is on your mind?

I dated my ex for about 2 years. We broke up about a year ago. I have gone through the grieving and the sadness and I feel okay, but they still cross my mind pretty frequently. I don't necessarily miss them and I do not want to date them, but why are they continuously in my head? It frustrates me because I feel like they shouldn't be and I don't want them to be. Hopefully someone has some helpful insight/advice for dealing with this. It isn't fun. 

2017-04-11T00:37:33.809Z