I don't want to be with him but i don't want him to be with anyone else?

You don't actually like him like that. You just like the idea of him liking you, and you got jealous because maybe you thought you were the only one he was interested in? Doesn't work this way for guys. You need to understand that need to have multiple love interests or the "loving" will never actually occur for us. It's because of all the indecisive women, game players, uninterested women, that we have to have multiple options. All I can say is, if you are ever interested in a dude, and you want to hold on to him. Tell him your interested, or else face this situation.