Heh, Draco might be afraid of getting punched in the face- or worse- if he does. :)

Draco's ego is still so very intact that he hasn't yet thought Harry may really succeed in leaving him (either by wounding his ego deeply or simply running). As for swearing off sex, well, it made sense at the time?

Harry does think sulking is part of his real personality, yes (partially because it's unattractive).

Next chapter is in a few days.