I've been with my boyfriend for a bit over six months now (knew him for a year before that), and part of me wants to tell him about my trichotillomania and the fact that I'm in therapy for it, but I'm scared.

Other than therapists, I've never told anyone about it before - my parents know, but they're not particularly happy about it, and dad especially didn't react well to me being in therapy when I was younger so I haven't told them this time.
It feels wrong that I've been with him for this long and am still keeping what feels like a fairly big secret from him, but I don't know how he'll react and I'm worried that he'll see me as some sort of freak.

Things are going very well between us and I don't want to mess this up - it's by far the best relationship I've ever been in - but it's come up in conversation that I've been going to the doctors fairly regularly (I haven't told him it's a psychologist I'm seeing there), and although I told him at the time that I didn't want to get into details because it would take a lot of explaining, and he said he understood, I don't know how much longer I can keep this up. I don't want him thinking I don't trust him, and it would also mean a lot to me if I told him and he took it well.
Any advice would be much appreciated!