I think in this situation, as i see it he does not want a serious relationship with you..That's the main thing here to realize.You do..So already there's a permanent problem that will not solve itself.My advise is to not call him,not accept any of his calls.Continue to tell yourself THAT IT'S OVER. tell yourself that many times a day.most of all no matter what,do not communicate with him.I know this sounds sad right now but for you in the long run it is the BEST thing.it is really the only way to stop the obsession. If you have to tell him to stop calling once and for all then do it..It may not seem like it right now but you will in the future detach yourself from him and meet someone who you can be with happily..The main problem with obsesions is the want need to communicate and it's much worse in this situation where he is also just inviting sex.Stay away.

take care...