I saw your pic, you are not fat. You are nice looking. Maybe he is looking for a model with six-pack abs? Does HE have six-pack abs? If he doesn't, he shouldn't ask for what he ain't got. I think sometimes guys get caught up in searching for, or making, their fantasy girl, the perfect girl for them. A hot bisexual chick who pole dances, or some silliness. I hope he gets out of this rut.
I mean if you were so heavy you were a danger to yourself, as in, you'd probably die of a heart attack in your 50s, then it might be a reasonable request. You are not fat at all. You are just right.
I have a long time interest in psychology, specializing in relationship dynamics for 30 years.
(Please note, we give the best advice we can based on the information given in a post. For better advice, please include the age of all romantic partners.)