I'm not going to tell my best friend that I accidentally outed him to four people
Is there a reason why you would want to hide that from him?
He would be very mad and might want to hurt me.
He may be mad at you, but I don't think that he would hurt you. Nonetheless, you shouldn't share your friend's secrets with others as it is a breach of trust in your relationship and could cause a rift between you.
I didn't tell them to hurt his feelings and I don't want to risk being hurt by him.
Maybe you should just tell him the truth then. He is going to be less upset if he hears it from you than he would if he heard it from someone else.