What he has shared with you and asked you not to share you could use as a way in to tell him about your problem. "You know how you told me X and asked me not to tell? I have something I'd like you to know about that makes me uneasy and for which I'm seeing the doctor all the time, as you've noticed." Just doing the set-up and pausing will tell you a bit about how he might take it? If it looks bad or it is too difficult for you to go on, just continue with "It is too hard for me to share with you right now. . ."

When I get cornered about something that embarrasses me, I say "to heck with it" and "give up". At Uni my dorm was an all-girls dorm and had a Secret Santa thing around Christmas and we exchanged small gifts during the week with clues and then the big gift on the party night and revealed ourselves. The person who had my name happened to be my next door neighbor, who lived in a singleton, her own room, no roomies. She gave me a great bra and pantie set and I immediately put them on and went over, knocked on her door and went in to show her. She wasn't in her room but her boyfriend was :-) Oops! LOL. What can I do? I reframed it; fortunately the knickers were patterned and like a two-piece bathing suit so I went ahead; I have three brothers, had had boy friends, knew her boyfriend wasn't seeing a girl in her knickers for the first time, etc. so I modeled them sweetly for him, turning around and acting like I was on the catwalk :-) Victoria's Secret would have been proud.

Do the same. What is trichotillomania about? Hair. So? So you pull your hair out, tweezer your hair out, have bald patches. Unpleasant, compulsive, habit. But it's just hair! A lot of the bad feelings are yours rather than other people's. Someone who doesn't have any vices/bad habits and is uncouth might make fun or be repelled, but not someone who likes you and has been getting to know you for six months. He may already suspect? One can't hide things forever.