One of my ex's was asexual, but in sort of an interesting way.
He found himself capable of being attracted to things on an illustrated, or conceptual, level. But at the same time was repulsed, or rather afraid, of the physical act. He considers himself asexual cause that's the best way to describe it, he has no interest in physically doing anything, even if he finds the concept attractive.
So I think the problem between Nic and Mortimus is more what constitutes as an asexual. And what I think Mort is trying to say is that sexuality is not based on act, it's based on attraction. While one may participate in a sexual act with a male, that does not make him necessarily attracted to males, and yes there are a lot of situations where people will have sexual relations with people they aren't attracted to (A gay person doing stuff with a girl, even marrying, cause he's afraid of persecution. Someone experimenting with a different person to check things out, a man getting raped by a girl, etc)
So asexuals can still have sexual relations with someone and maintain their status as "asexuals", even if it's just for pleasure. Another example is some sexual participatory acts have the same form of participation regardless if the partner is male or female. So if you blindfolded one of the partners, the act would feel the same whether or not the person on the other side was male or female, in this way a gay person can do stuff with a girl or a heterosexual do something with a guy and still maintain their sexuality, cause they're enjoying it based on pleasure alone, not on attraction.
Maybe that clears stuff up? I want to point out the sophisticated and analytical vocabulary here, keep it, so it doesn't necessarily break rules talking about this stuff.