<human>: Me and my gf have a FANTASTIC relationship, we see eye to eye on so many things and I can't imagine being with anyone but her. Being with her is pretty much everything I've ever dreamed of in a relationship. But since we have been together she has let herself go to such an extent I am losing sexual interest. In her defense she had a severe spinal cord injury and it is difficult for her to excersize, but she does no favors for herself in how she diets. She was a curvy girl when we started dating but has since gained over 50 pounds, pushing her well into the overweight category. The last time we had sex I actually had to pretend I was having sex with one of my exes to stay hard. This is really starting to get to me, I REFUSE to leave her, I love her more than anything, but lets be honest, when sex goes it causes a relationship to go stale. I managed to tell her that we should diet, and she is eating a little better but the weight isnt coming off. I'm not 100% sure of my question but I guess... 

How do I deal with loss of sexual interest in an otherwise amazing relationship?

Could you distill the essence of the text into 1-3 sentences?
<bot>: Gf has let herself go (though not entirely her fault) and I have lost sexual interest in an otherwise amazing relationship.