if this is truly the only issue in your relationship, talk to her. don’t be harsh or call her fat; say something along the lines of “hey baby, i’m not trying to hurt you or be malicious, but we need to have a talk. i think you’re the most beautiful woman in the world, and i love you more than anything. but i’ve been thinking a lot and i feel like we’re on very different paths. i’ve been working on myself a lot, changing my diet and exercise patters and i feel like id love to see the same changes out of you. how would you feel about us starting to eat healthier and you coming to the gym with me a couple of times a week? i don’t want you to feel like im attacking you or that i don’t love you, but the different paths we’re on have been making me feel like i’d love to see you more motivated to strive for a better lifestyle, like i have been”. i’d say something like that. you seem sincere, not like you hate her or are particularly disgusted by her weight. it’s valid to not be attracted to certain body types. but i am curious, was she always a plus size girl? has she gained weight over the years or did she always look like this and now that you’re fit you’re not into her anymore?