What should I do in a new dating situation about the ex-girlfriend?

I recently started dating this guy who recently got out of a two year relationship. We were acquaintances for a year and got to be better friends over the past few months before we've started dating. The issue is that he's still in frequent contact with his ex and they often see each other, even though its platonic now. Still it makes me uneasy. I'm wondering if this is normal or if I should say something about it. The reason I hesitate is that we're not exactly serious yet so objecting seems a little weird. I think he's a great guy and I know that he wouldn't do anything to hurt me by going behind my back and doing something as cliche as that sounds. Its just that in my last relationship, my ex ended up going back to his previous girlfriend and I just don't want to be in the same situation again. I don't want to be naive this time around. Any suggestions? Thanks a lot