two scenarios:
-you appreciate the few extra pounds (my bf LOVES being able to grab a fistful of my posterior and win in the situation
-you find yourself losing attraction for your partner. certainly her personality attacked you, but it'd be idealistic to deny that part of what attracts us is physical. the best way to handle it if you would like her to see if her original size is still attainable is to lead by example. a lover is more likely to start taking care of their body if you're AT the gym with them, running with them (not to mention the smut-fest when you guys shower off together!), eating better dinners, etc... women's weight is much more complicated than ours and maybe harder to control because so many causes of weight gain/loss are out of their control.
in the meantime, try to focus on the other aspects of this woman that attracts you, but your feelings are completely valid and should be discussed with her. she may be embarressed about it and afraid to talk about it so opening the door may be on your hands. | 
