I know what you are talking about because i was in your shoe before
your girl friend reminded me by me ex girl friend. I was in good shape but i have a little bit extra fat in my billy so she always made me feel bad for that, sometime when we made out or sleep with her i cant take off my shirt because i don't feel secure about my body anymore
During the relationship i start to gain weight more and more due to the hard time she gave me about how i look. Many times she wanted to break up with me and her reason was you ate not healthy!!! i mean come on am a80 cm and weight 86 whats not healthy in that!! Now believe me this kind in relationships is not healthy and they use your energy and happiness after they done with you they will look for another person they just like a vampire, you are better without them.