You need to explain to him in a way that he can understand that while at some point you all may be able to resume the friendship you had, right now is not the time because the situation is just too new.
Let him know that you need some time, but will always be there for him in the best way that you can. But right now...you can't be friends. It hurts too much and its making it impossible for you to be happy. If he's truly your friend, he'd want your happiness to be the first priority.
If he can't take a hint after that...well...just be rude and stop speaking to him altogether. Avoid him. And if that doesn't work....just try not to end up on a Lifetime Movie.