Why am i still having these feelings?

my ex bf of 5 years and baby daddy has a new gf and it really is bothering me. we have only been broken up for 4 months. i jumped out of a relationship with him and right in to another. my new bf is awesome i love him very much but he hates when me and jayson(baby daddy) talk at all. even about ev our child. he wants him cut out our life completely. and i can't do that to evelyn. she is only two and loves her daddy very much. i am still friends with jayson. i enjoy talking to him. he is a good friend and listener. we dont do anything sexual anymore of course. but idk y him having a new chick bothers me im really sad by it what should i do? just push it to the side and not worry about it and move on with life or what.