I have a friend who is obsessed with me. he self harms and cries if im not there. but sometimes for two weeks at a time, he stops caring about me. ??

Move on: The only person you are responsible for is you. If he contacts you suggest he get a life coach/therapist to learn how to deal with life. You might consider doing the same. It may be flattering to have someone obsessed with you but I know of too many cases where that behavior led to a fatal event to suggest you ignore it. Get out of that cycle & stay away.