Most Helpful Guy
From this kind of behaviour it seems that he is obsessed with you. visibly he is trying to get your attention and trying to keep an eye on you. though he once used to date you, he doesn't want to get off from you. may be he is trying to get back to you again. talk to him about this or ignore him. may be these kind of stalking can get more ugly. better to sort this out and talk to him about this directly.