BlueJay, your W's sexual assault very much plays into her feelings about her own sexiness, what she deserves in a man, what she thinks will make her happy, etc. Do not discount this!
It could be that at the time she married you, she did not see you as a man who would have much in the way of sexual desire... because of your weight. It's very likely that she fell in love with you because you seemed safe to her. This is not a bad thing. Partners need to feel safe with each other. Walking the line between safe and "dangerous" (as Mojo described) enough to be sexy is tricky. It's the subtext of a lot that we talk about on these boards.
Then when you lost weight and became potentially and then actually a guy who was going to WANT sex, she may have felt subconsciously that you had broken the deal. This is just rampant amateur psychology on my part-- I don't think she intends ANY of this. She's just scrambling for survival... with this gaping wound, and precious few emotional/spiritual resources.
Your anger is totally understandable... but staying stuck there will not be good for you. You have 50+ years of life ahead of you... you're too young to give up. (I know you aren't really giving up... you're just venting right now. ) There is help for you out there. There is help for her, too, but she has to see it and be interested.
Sometimes when one partner goes to therapy, the other partner sees such a change that they get curious and become interested AS LONG AS THERE IS NO PRESSURE FROM THE FIRST PARTNER TO GO TO THERAPY.
You have nothing to lose by confronting these issues (yeah, she picked you and let you down, but YOU picked HER, too...) with a professional. EVERYONE has issues. It's not a case of mostly healthy people walking around and a few screwed up people messing it up for the rest of us. We're like pieces of a puzzle, and we attract people whose puzzle pieces fit ours.