Basically, I think in the "nice guy" situations, both parties are at fault. The male needs to nut up and ask her out and establish interest, and the female needs to make it absolutely clear that it's not going to develop into anything else.
It's possible that the friendship might not last after this, but it wouldn't have anyway. The issue I see is that both parties seem to be too afraid to ask for what they need in their interactions with each other. An injection of courage into one or the other of the individuals involved would simplify these issues.
As for "wanting sex" so what? Most people like having sex, the only issue is that they like having it with people they are attracted to. The only reason why this is objectionable that the nice guy wants sex is that the women isn't attracted to him (whether it's physically, or because of personality) . Which is fine, but this doesn't really imply anything about the character of the "nice guy" other than the fact that he needs to practice being more straightforward, assertive and less of a wimp.