Can't get wet or aroused. But I need sex!

Ugh. My boyfriend and I have been exclusive for the past two years basically. I'm only 19, but I feel like a 40-year-old pissed off woman who had her sex life and is now done. I think sex is a healthy part of life. It's beautiful and exciting! But nowadays I cannot get wet. I'm a firm believer in sex. I love it, I need it, I think about it constantly but I wish our relationship in that particular area could go back to where it was. My boyfriend is on antidepressants, and yes, I understand that certain medications may destroy one's sex drive. But now I'm worried about me! Because it has been about four months now that we haven't had sex. After pleading him to give it to me, I was surprised at what concluded. I made him stop. It was killing me! (Because I wasn't really aroused since I suggested sex randomly and out of the mood, but no matter what I could not get into it. I couldn't get wet and I went raw quickly.) Basically, I first needed advice on how to spark up his tragic sex drive. Now, I'm worried about me. I was so turned on when we met. I love to be sexy for him. I'm the type to do the whole outfit game. But as soon as we don't have sex for a few days, we lose the sight of intimacy all together. Help. I love him. I want to marry him, but it can't be this way forever. And if that's how it will be, then how could we possibly work?