Body image can surely be a touchy subject. People may gain or lose weight for many different reasons, and in the era of the Instagram model, it can all be so discourageing. Men are aware of this and sometimes just don't want to hurt your feelings, so they'll keep their thoughts about your physicality to themselves.
If your body has changed from when you first started dating your man, you may want to have a conversation with him about it. Or maybe you don't. Just remember that despite how your boyfriend may secretly feel, you come first. Love yourself and focus on being the healthiest version of you for YOU.