OP you need to woman up and speak to your DH about how you feel be supportive and kind to him .
My DH is overweight he just loves food, but he has always been big when he actually went down to his 'correct' weight he looked ill, he is very broad chested, he goes to the gym but he will never be small, he has been bigger and he lost about 5 stone a few years ago but it was because he wanted to, I love him any size he is but I was worried about his health so I would try to gently encourage him and eventually he saw it for himself.
I'm not small either, I was much smaller before I had my DDs and thank goodness he still finds me attractive eh? 
You do sound very focused on your DH's weight and it reminds me of the way people make excuses/focus on one bad habit when they want to break up with someone.
I personally find it very strange that the main and only sexual attraction you have towards your other half is just his body shape you can feel however you want but I think you should ask yourself why you feel the way you do.
I find my DH fanciable for various reasons yeah he's fat, I'm fat too but he's generous, he's handsome (according to me), he's strong, he's protective, he's funny, he has nice hands and long lovely eye lashes, he's a good dancer, he's caring and gives a mean back rub, he is also extremely considerate in the bedroom, all these things make me fancy him, moobs and big belly aside there is more to fancying someone than their physical appearance!
I hope things get better for you both just try to be understanding, wishing you the best 