Maybe

"Maybe Remus didn't know the effect he had on Sirius. Maybe he thought Sirius was so used to the sight of naked bodies that it was harmless to let him assess every inch of his skin to fix the post-transformation damage. Then again, Remus should've known better than to expect Sirius to not associate a naked body with impure thoughts. So maybe he did know." Wolfstar UST. For Sylvia.