I've talked about some pretty embarrassing/awkward sexual stuff with my T--not BDSM, but a sort of fetish thing I have that's not particularly mainstream (something I think about, don't actually do). I actually emailed him shortly after that session to make sure he didn't think I was weird or disgusting (he replied pretty quickly). And just about some of my sexual experiences in general, in the past, with H, etc. It was awkward at first--I tend to stare at the floor while talking about it, and, much like you, I felt like I'd die of embarrassment the first time he said "masturbate" (I kept using euphemisms). But it's gotten easier the more I've discussed things. It also helps that he's very matter-of-fact about it, like he doesn't seem embarrassed or uncomfortable at all. Like you, for a particular situation I discussed (a rather disastrous attempt at roleplay with H), I was afraid he was sitting there picturing me in the outfit I said I'd worn. But I got through it. And I'm glad I was able to discuss it, because some of it tied into other issues I'm working on in therapy, as it sounds like it does with you.

I'd just preface it by saying this is really awkward for you, you're worried about his reaction and judgment, try going from there. Good luck!