If he leaves because she's gained 50+ lbs, there would seem to be a few problems going on. A major change in someone's appearance might indicate a change in their personality or lifestyle. Why has she decided to not stay at a healthy weight? Maybe she's stress-eating because of different factors? Also, if he has a problem with her gaining weight, why not say something sooner. People don't just wake up with 50 extra lbs. Also, let's say he's turned a blind eye to it and one day he noticed; wouldn't it make sense to have a talk about it and give her a chance to lose the weight? Did he gain weight as well, over the same period of time?