The other tightens on her hip. It might seem like it's so he can control this but really, he's trying to resist his body's desire to just give in and move, properly, to relieve this ache.

A bit more, though. A bit faster, but only to match her speed. He has to breathe, and it chokes out of him as he pushes up, louder than he intended but he can't help it. This is torture.