To be honest, it completely depends on you.
I mean, even if you're not asexual how important sex is to a person really varies. Some people can't imagine living without it for so much as a week, some are fine with having sex once a month or so, some enjoy sex if the situation leads to it but don't go looking for it, etc. Sexual attraction isn't a binary thing. So, really,
you have to be the one to figure out if not having sex is a sacrifice you're capable of making.
There's also the possibility of an open relationship, or one where they're fine if you go out and have sex with other people provided you don't get emotionally intimate with them, but that is /really/ not something that works for everyone. It's also possible you might be able to have sex, but this completely depends on the asexual person - in any case, it would be something done for your sake rather than theirs, but some asexuals are really pretty much completely neutral on sex and find it more boring than anything else. If they're one of those people, they may be willing to occasionally have sex with you so you don't get too frustrated. Of course, the spectrum goes all the way to "ew that is completely repulsive get it away from me", and in that case you're out of luck.
The one piece of advice I have for you is -
don't assume this is a phase. I mean, it might be, but there's absolutely no reason to think it's certainly the case. And the fact that a person wants a romantic relationship doesn't mean they're any less asexual (the asexual community talks about romantic vs. aromantic, and there are a bunch of romantic asexuals), the fact that they might masturbate doesn't mean they're any less asexual, etc. If you go into it with the expectation that they will one day want sex, that's just... poisonous, since if they /don't/, you may very easily grow impatient or start pressuring them without meaning to. And, to be honest, if /they/ get the impression you're basically sitting around and waiting for them to develop a sex drive... if I were the asexual other, that would be the end of that relationship.
Assume going in that they are genuinely asexual and will
never want sex. If it /is/ some kind of phase, then you'll get a nice surprise, if it isn't, you at least won't be disappointed.
If you really want to know more/want advice about this matter, I urge you to check out
AVEN. Really, I cannot stress this enough. AVEN is the biggest asexuality site on the web, they have a lot of friendly and welcoming forum-goers and this is the kind of question they excel in; this is a very, very typical situation among asexuals, after all. There are even a bunch of sexuals on the site who are in exactly your situation, and the asexuals can give you a view of the opposite side of things. In any case, /all/ of the respondents will be very informed about asexuality and what it entails, which a lot of the respondents here, uh, not so much. (For instance, a point that's been confused a lot here - it /is/ possible to be asexual and get aroused. The person just has absolutely no interest in acting on that arousal with another person.)
I'm asexual, although I'm aromantic so I can't really help very much in this! However, if you have any questions feel free to ask or PM me.
Quick edit: the above should make the reason I'm not answering your question clear *g* since for one, I'd be the asexual in the relationship, and for another, I'm not interested in relationships.
And after getting further through the thread, I see you've already been to AVEN. Great minds think alike! *g*
