This is probably one of the biggest paradoxes between sex and Christianity. Lust and sex are bad. But it's also bad if आप don't have babies, even though शिशु can only come from sex.
The Bible doesn't give very clear consensus about whether या not Asexuality is a sin या not. Beyond men having sex with other men, the Bible doesn't say much about sexualities at all. (Not that it really matters, because आप shouldn't be basing all your morals based on one book anyway.)
I don't think any type of sexuality is a "sin", so long as you're not harming anyone with it.
EDIT: लिंक्स about Paul:
link link link