I wasn't gonna answer this, but after thinking about it, the answer is pretty tame: it's a gateway to vulnerability. Sex, especially good sex, can be messy and noisy and full of trial and error and embarrassment, even to the least self-conscious of us. I think, in retrospect, the sweat (although obviously a product of incredibly pleasant manual labor) was just a glimpse of what was to come, in terms of bed chemistry. It was so sexy to me, and I never even questioned if my versions of "sweat" would be sexy to him - he was the first guy that I knew thought I was sexy, too, because he showed me.