Wife's low self image is ruining our marriage (and sex life)

I love my wife. I've loved her for over 20 years. She's beautiful, funny, witty, kind, considerate, and my best friend. Except when she goes to her dark place. My wife has problems with frequent bouts of depression. When she's in one of these funks, nothing I can say or do will help. She gets 'body image perception disease'. She dwells on everything negative. She checks out. It's as if she's been replaced, by a pod, like from Invasion of the Body Snatchers. My awesome wife is gone, replaced by an alien whose sole purpose is to suck all the joy out of life, both hers and mine. I gave up trying to fight this years ago. Like I said, nothing I can say or do helps, ever. She just has to ride it out. But I'm getting SO DAMN SICK AND TIRED OF IT. And it makes me feel like a jerk, because I should be more understanding... But it happens over and over and over and over and over and over again. Yes, she's tried meds. They even her out, but then she has no sex drive. Yes, she's tried all the different kinds. Last night we were drinking a little bit, and having a good time watching old music videos from the 80s. We were talking and laughing, it seemed good, and one thing led to another. All of a sudden when things were getting good, she starts covering up, not wanting me to see her. It ruined it. I just stopped and got dressed. I don't know what to do any more. I don't want to leave her, but her problem is literally driving me insane. I'm not getting what I need, and I'm starting to really resent that she's so damaged. Am I a jerk or what?

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