I have just dealt with this problem recently, and I have found out the answer! you must be around him for awhile then, for no reason leave, just kind of avoid him. Show that you have a life, don't always pick up the phone when he calls and take awhile to call him back. Then, just when he's about to lose interest, (let's say 2 weeks) then be around again. It'll drive him crazy, because you know that "time makes the heart grow fonder". Then, compliment him all the time, build his ego up. Suggest things you want to do around him, such things like "I want to go see this movie, but I don't want to go by myself" hint around that you want to do stuff and if he likes you he might go with you. Do unexpected things, like dying your hair, changing up your look, style, this will excite him (not in a sexual way) and he will associate being excited with you.
Men will always want you if they want you once. As to go crazy I assume you mean sex? Try talking sexy on the phone. That works for me. Tell him how much you want him and think about him. The other side of it is either he is a dominant or submissive type of personality. If you know then you are in the drivers seat... Play to it. I don't mean tie me up tie me down stuff... I mean find out if he wants you to jump on him or if he wants to jump on you. If he is a good boy he may want a bad girl or just the opposite. Play to that and some great sex should happen ;)
I would say at least a few months. Why would you ever want to torture somebody like this?
Everyone is different. Sometimes it'll take a guy a month to get over someone and somtimes it'll take a year. It all depnds. And as far as making a guy go crazy for you then you need to do a couple things. Be nice, fun, outgoing, confident, and take an interest in some of the things he likes.
Driving a guy crazy?
If you liked a girl at one point, how long would it take to stop liking her? What could the girl do to make you go crazy for her?