>>1
I'm sorry to say this, but when you tell him this it is going to hurt him and you (if you've invested enough emotion into the relationship).

Unless he's into that sort of stuff, there isn't much you can do to keep a relationship with him and the best you can do is break it off with him without him knowing because there's no telling what he'll do when he finds out about you.

I'm probably being too negative, but these sort of situations don't usually work out.