I accidentally told my boyfriend's friends that he has IBS/wears diapers. He won't talk to me.?

I am sorry if this sounds harsh, but he is very serious about the disaster. Leaving your phone was not an accident -- It was your thoughtlessness or worse. I don't blame him a bit. Neither should you since you broke his trust in a very serious way. He will never get into that frat, and your negligence is the cause. You can't take it back and no explanation will help. It would be nice for you, and maybe for him too, if he would forgive you, but you shouldn't expect it.