This is a rough one. I'm going through a separation leading to divorce right now, and while there are a lot of reasons for it, a large contributor was the realization that I was never going to be happy fat, and he was never going to be happy with me trying to be (and hopefully finally being) thin.
Hopefully everything will work out for you, but I wish I had realized this years ago at the bottom of my 30's instead of the top.

cake being offered over and over.
She is overweight also and I think it's the same thing you are talking about with your boyfriend, a combo of guilt and maybe even fear of being "left behind"