Is he underestimating the man below him? Perhaps a little. But new as this is, and because he knows he is stronger and can withstand more, it is better to err on the side of caution. But, John has a wonderful way to assuring him, and he won't argue, and he doesn't need to be told twice. He learns.

Reaching down between them to steady himself, he starts to press inside, slowly at first put as John relaxes it gets easier to slide in, burying himself to the hilt inside the other man. He takes a moment to breathe, to simply enjoy the feeling of the tight fit and the heat surrounding him. Then he starts to move, with slow, deep strokes of his hips.