Advice: Unconventional Wisdom

It may be that your friend has interests that he feels he can't share openly with you, a curiosity about what might be labeled "alternative" or "kinky" sex. Don't you want to know? Don't you want an emotionally close relationship where you feel you can confide your thoughts and interests to each other without fear of censure? No one is saying you have to perform any acts that are distasteful to you. But human sexual interest is extraordinarily diverse, and it's healthiest when it's openly discussed between two people.