How do I handle these feelings?

My fiancé and I of 3 years have been TTCing during that time I had a miscarriage. Last night my ex out of the blue requested to follow me. He and I planned on having a baby but I broke it off because at the time he was verbally abusive. Then I saw the girl he started dating after me is pregnant. Something made the feelings I have a lot of days come back of still missing him and wanting to get back together. How do I make the feelings stop of missing him?