to be or not to be

My bf of 4 years has a older brother who he has a gf/baby with the cousin of my bfs ex gf so the ex gf is always gna be around when it comes to the older brothers kids bday etc. but even though my bf says he no longer has feelings for the girl im still bothered by it and get a little jealous when i shouldnt be . should I worry or waste my time trippin on his past first love?.?.?