Sorry, but he's a twat of the highest order!! Everyone who's replying going 'ooh maybe he's got a point dear, try some calorie controlled milkshakes' is missing the point! OP is spiralling downwards, she's grieving, depressed and on her way to developing s serious eating disorder ffs. Her DH knows this but still tells her in the cruellest way.
I agree that the problem lies with him. In my experience, if you start to go off someone it's very difficult to get back to feeling attracted to them physically. I very quickly go to 'no don't even touch me!', no way would I want to have sex 3 times in a weekend with them (good going btw, me and my DH fancy each other but it's been a long time since we managed anything like that thanks to small DC!)
My point is, he's inconsistent, clearly frustrated about something, rather than unpack what that might be, he's cruel to the OP - who is not just sitting back stuffing her face, she is actively losing weight and is the first to admit she's gained!
OP, I'm so sorry for what you are going through. Please try and look after yourself, eat something, you are worth so much more than this. Maybe call BEAT or another eating disorder helpline? There is help out there...focus on you and then decide what you want to do about your relationship. Good luck.