The idea that Will is somehow asexual because he didn't toss Elizabeth and have his way with her at first opportunity is kind of ridiculous. Along with the unwanted pregnancy aspect, is the socially aspect, and considering their circumstances they were likely gist for the gossip mill as it was.

Will controlling himself is likely more about respect for Elizabeth and her father and preserving their (likely tattered after the events of CotBP) reputations, as it is about any lack of sex-drive, or sainthood, on his part.