Is he on medication? That can right royally feck up sex drive depending on what he's on of course.
Has he ever had a sex drive? or is this a constant non thing rather than a temporary glitch?
Some people just have a very low or non existent drive, maybe you skipped having that conversation where you talk about what you want and need in that regard.
If he is physically capable, masturbates, looks at porn (has an interest in sex), but cant or wont get aroused with you, then you have problems. If he likes porn, what type? You dont sound the type to tolerate it btw.
Maybe your gaydar doesnt work? You missed the aspergers after all. (sorry)