There’s nothing wrong with sharing nudes (provided the recipient’s consent), but you should understand that along with your muff shots, you’re sending a message of potential sexual interest and/or availability.
I’d be a hypocrite if I advised you not to express your sexuality. It doesn’t sound like you are trying at all. I don’t mean to interrupt your merry, nearly nude traipse through life, but a good way to set boundaries is to actually set them. But I also don’t want him to try to come on to me, because rejecting him in that scenario would also be awkward.
How can I keep clear boundaries without hurting his feelings? Flat-out telling him I’m not attracted to him seems like it will kill the vibe.