Well, to be honest, I haven't delved
that deeply into the 'vows' specific to the Sifu's order buuuuut, if I vaguely follow the paths laid out by the martial monks of Shaolin or whatever, I'd imagine there's a vow of celibacy involved
somewhere along the lines...
...hey... wait a minute... It actually looks like Buddhist monks take a vow to 'refrain from sexual misconduct' not necessarily abstain from sex all together... interesting...
...anyway, vows and such aside, I don't imagine that our little monk has really experienced anything sexual in his life beyond a kiss. Spent a lot of his early years as little more than a 'trained-dog' for Chap (and getting his pit-bull bedded wasn't high on Chap's list of priorities). Following his escape from Hoskins, Fu Sheng likely didn't have the social graces needed to 'win over a girl' (not that he was really looking, at the time) and was more concerned with finding his way back home or, at least, finding his family. Then there was the monastery... then the orphanage... *shrugs* Vow of celibacy? Not that I'm aware of... Virgin? Absolutely.