Why does this bother you so much? It doesn't make him gay, or bi or anything (although I dont know his sexuality). It doesnt change the person he is, think about it this way; he liked a dildo in the ass before you found out about it and you didnt think anything weird of him so why should you now? I understand that it's a shocking thing to hear about your friend, I guess but it doesnt change who HE is. He's just kinky, you'll get over it.