Relationships will only work if one accepts the other for who they are, and not because of the way they look, or behave, and vice versa. Marriage, Friendship, etc. that how it works.
You may have to kiss your man goodbye, because for me, it feels like you're done. But there still are many doors for you because you're young.
But, try to understand his drive to change his body image first, because you may learn why. Your relationship with him may evolve into a strong friendship, and trust me, it works too.
Good luck!
K