Or do you mean spying in the bad way, like a stalker? Is his behavior creeping you out? Some guys do have unresolved feelings about old girlfriends and are unable to move on. I don't know any details about the break up or if he is the obsessive kind of person. You called him a friend, so I assume that he could talk to you and ask you out if that was his intention. He certainly should know you well enough to do that if his used to be your boyfriend.
Like jennys said, "Go with your instincts".