Honestly, that is very shallow. That should not be a determining factor to leave someone. If that really is the case, he deserves more than you. You should love someone more than looks, when you guys get old, you won’t look like you did when you were 20 and what you are left with is their character
No it's not bad. Especially if you're no longer attracted to them anymore. And also if you've hinted at your ass is fat can you please lose some weight. If you wanted to be with someone fat you would be. It's not even cool that he let himself go like that. Men leave and cheat on women all the time over this. Women can have these same feelings too