Boyfriend Friends W/Ex-Girlfriend

Ladies I'm usually not a girl that really cares about who my boyfriend hangs out with , we have a very open line of communication we talk about everything , it's just this one Ex that he is really close with and deep down it kind of bothers me he gives her advice about relationships and they hang out and one time I found out they where Facetiming and it had been going on for a while and we talked and Im over it but it's just I don't know how I'm suppose to feel about him being best friends with his Ex ?