Yah, tell her this:
You: You've been working really hard in the gym, I really absolutely enjoy (emphasis this strongly) working out with you. (even add in a little joke here, for example, "watching you do those squats turns me on")
Her: *Most Likely* Haha (if you said joke), thank you, I like working out with you too (something to that nature and it would be cool if she said "I wish you wouldn't work me out so hard" sexual reference, go bang her in the showers at the gym,
)
You: You know what would really help you now, working on your diet, I think it would help me stick to my diet better if you kinda followed one with me, think about it, you and I working out and dieting together, it will make us stronger and healthier physically and strengthen our relationship. (Be sincere, it will work, but its all in how you look, strong eye contact into her left eye, don't let your eyes shake, that means insecurity and she might feel an underlying message).
Her: ok, blah blah blah
You: You know what, I like seeing you on that bench too, haha
(go have sex)
Success
-If you do this please tell me how it goes... I think it would work. It can't hurt to try, if she flakes then game over, you said yourself the relationship wouldn't last, IMHO her flaking would be good, if she tries, then I still think your screwing yourself, because when she does lose weight you are going to feel more OBLIGATED to stay with her because you changed her, either that or she leaves you. But there is always that chance that it actually does strengthen your relationship, love can be built.
EDIT: Also, dude your from Charleston! I'll be down there in the fall, if it doesn't work we can wing and game like crazy, haha!
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