Bad Jealousy

Hey guys,

I need some advice.

I am a single mother and I am dating a single father, our kids are 6 months apart in age.

Anyway, I am completely for exs getting along for the sake of the child etc. But for some reason I am becoming extreme jealous every time my SO mentions something that leads me to believe he still has some feelings there. Like today he told me he got angry at her because her boyfriend is moving in with her. I asked why he'd be upset with that and he said it's because they hadn't been dating long and he doesn't want some stranger living where his daughter visits (my SO has most custody 80%) and i get that believe me I understand why he might be concerned but for some reason every time he mentions his ex my blood boils. He has assured me he doesn't have unresolved feelings for her and he only wants to be with me but I don't understand why I am being like this. . Has this happened to anyone else?? How did you deal with your jealousy? I know this is completely a 'me' problem but I can't help it and it's starting to bother me. 😣