My boyfriend keeps peeking at his Ex-girlfriend's Facebbok profile - should that bother me??!

My boyfriend juat loves Facebook, and he has this hobby to check out his his Ex's profile! It happened at least 3 times, and maybe was more times that I'm not aware of. He says that he's just curious, but I'm still not convinced. Am I just being paranoid, or should I be worried that he still got feelings for her?