Yes, sex is absolutely a basic need. Without sex, I get low self-esteem, depression, feeling of being trapped, masturbating over and over repeatedly without ever feeling any relief... it's just not good. I don't know whether women need sex as much as men, but I can say that all the women I have been with for longer periods tend to enjoy sex for about the first 2 months, enjoy it occasionally for the next month or so, then completely lose all interest, and that interest never comes back. Maybe this is not a representative sample, but it is consistently my experience.

As for your situation, this guy is a saint if he has gone a year of not even ever seeing you and he is still (figuratively) by your side. Why would you even consider withholding sex from him when you see him? He has stuck around for a year with absolutely nothing. He's clearly not using you for sex.

As to your depression, I have been in your situation (but not for anywhere close to a whole year) and realize that it's a feedback loop. You lay around and don't do anything because you feel worthless and depressed but laying around not doing anything makes you feel even more worthless and depressed. You already know this, I'm sure, but you have to actually do something to get out of it. It doesn't just go away. You feel like you don't have the energy or the motivation to do something, but do it anyway. I mean something as simple as making yourself walk down to the coffee shop and eat a bagel every day. But you have to force yourself to do it, really force yourself no matter how tired or unmotivated you are, being out in the world will help. And actually agreeing to meet this poor guy who has stayed with you for over a year of your refusing to see him will help a lot too, I imagine.