My husband is jealous of my ex husband

I don't know why my husband is jealous of my ex husband but he is. Bad thing about it we have both remarried. We have a great parent relationships granted it hasn't always been like that. Even though I didn't put him on child support, he still calls and talks to our son daily. It's my son's birthday today and his dad sent pics of him because he lives in New York and I live in GA. This caused a big fight with my husband and I. He doesn't want him writing, calling or sending anything to our son. Idk what to do.