Why did he stop contacting me all of a sudden?

have you talked to him about how you feel? if not then you might want to try that, then if nothing changes and your not happy then you really need to move on because its clear that your feelings don't matter to him. busy or not, people in relationships can always make time for each other and if you cant see them then you at least make sure you talk to them (and i don't mean once a week) more like every day or at least every other day. the "relationship" that you have described sounds more like friends with benefits than an actual boyfriend/girlfriend relationship. good luck to you