My friend has made some homosexual advances?

Well you made a big mistake in letting him do that to you, now he is under the impression that you are just closeted, and he has developed feelings. But as there is nothing you can do now, you just need to come out and say it. Tell him you are not gay, and that you do not appreciate his advances, and that if he wont stop then you can't be around each other. It may seem harsh, but sometimes that is the only way, being nice about it will just give him the wrong idea.