I don't know what to do.

I dated my ex for about 3.5 years. We drifted aparted and we broke up. In that time met my now fiancé and started dating. I moved into my own place in September of 2017, and been gone since then. I've seen my ex a few times to finish some business we had linked together. I find myself thinking about him and missing him but I'm completely happy and deeply in love with my fiancé and I don't want to leave or lose him. I don't know if I miss the some what attention my ex is giving me right now or what but I don't love him the way I did. I need help please.