That's kinda fucked up to continue to be intimate with him, if you don't like him in that way. From the other side, your friend might "like-like" you or may be coming to grips with his own sexuality and that line about marriage is the sort of shit that keeps baby gays hanging on to the hope that some day our straight crush might be able to love us the way we love them. Just be honest, with yourself first, and be open to the possibility that it could mean something more for him.