Redhead23 - What is wrong with someone being bi-sexual?
Nat13 - You've said yourself you don't want to be with him so you need to pluck up the courage to tell him so. It won't be nice for either of you but you can't hold yourself responsible for the actions of someone else, especially at your age. If you are really concerned that he may do something to himself you could try having a word with a friend of his maybe, asking them to check he is ok but remember he is not your responisibility and you have to do what you want.