Most Helpful Girl
Don't start putting on the pounds to please him. Any partner who would encourage you to be unhealthy doesn't give a shit about you, and that applies both to men who want extremely thin girls to be thinner and men who want healthy or chubby girls to be heavier. All you can really do is try to accept that he won't be as attracted to you as you'd like, or break it off and find someone who will appreciate you as much as you should be appreciated.
Most Helpful Guy
Why do anything?
He is into fat chicks he likes you enough to be in a relationship with despite not being fat...
Why is this a big problem?
What if you were a blond and he told you he prefers redheads?
Does it matter?
Unless he demands you gain weight just ignore it
So you don't get a top score on one of his preferences... no big deal