General

If she knows now you like larger women, she could be nicer to you. I once had a blind date with a thin woman who knew I liked larger women, and she wore clothes to make her look bigger. She doesn't have to gain weight, but she could acknowledge your preference. I agree that you should dump her. Not because she is thin, but because she is being mean to you.

She probably thinks that you see her as fat as you are dating her and you visit this site. She's probably feeling a bit insecure right now and the best thing to do is show her how much you like/love her.

Take her on a day out, do the things that she loves to do, or really wants to do. Remind her why she fell for you.

If you both love each other and have the right attitude then you will work it out.

I don't buy into this: dump them as soon as something goes wrong mentality that so many of us under forties seem to have.

You might need to reconsider a future with her.

If as you said, she gets very thin and you aren't attracted to her--then what? If your feelings for her would remain regardless of what she looks like, then the answer is easy. Let her do as she wishes as it will make her more confident.

If the answer is no, then your relationship will only bring the both of you grief.

If she was worried about her weight, but felt that she was thin enough to be acceptable, bf adoring her body and all -- then found out that actually she was FAT ENOUGH to be attractive to someone who likes really fat women, that could be pretty devastating. Worse if she finds out about feeders.

Think of it this way. If you were a slightly built guy but worked hard to be seen as more masculine, started dating a nice girl who was attracted to your body and that helped affirm to you that you were acceptably masculine .... Then found out that she was mostly into women, found some gender queer folk attractive, and thought that you looked just feminine enough to be interesting, but really didn't want you to get any more muscular or ever grow out facial hair, it might throw your confidence and self image for a loop.

What is done is done. So the question is, how flexible can you be about the future, and can she trust you in the future?

I agree with flyinghorse. How did your evening go? Over time, her emotional reaction may subside. Perhaps the two of you can explore why she has such strong feelings on the matter. From her reaction, I would guess someone to her said something to her that became a defining moment. I once read a comment here by someone that reached for a cookie when she was 4. Her grandfather scolded her saying "You don't want that. You'll get fat." That single comment sent her into a life of anorexia and nearly killed her. Fortunately she got help and overcame it and was able to enjoy getting fat now. Maybe your gf has a ghost from her past still haunting her.

Work with your gf - carefully, and gently. It'll be a process that takes time... probably a long time. Good luck and keep us posted :-)