Friends with an ex?

Sorry to post on this group but nobody ever answers on any of the other ones...So I just started dating my guy friend that I’ve known since elementary school (we are now graduated) and I know how he is and I was very skeptical of dating him because he talked a lot of shit in the past about his exes and he still talks to one of them every day on snapchat. It’s literally driving me insane thinking about why they broke up and why he’s still talking to her. I don’t wanna seem Psycho about it but I don’t know what to do, if I should tell him to delete her or what...someone please help a sista out!!😫