Wow, that's a gruesome tale. This is the greatest fear someone has when their partner says things like, "Honey, I want to lose 20 pounds." You can support them through all of their workouts, dietary and lifestyle changes, and the minute they look good enough they dump you for someone better. This sucks, but the only alternative is to not support your partner in their quest for self-improvement and then they may just get worse. They may get fatter, more insecure or whatever. So, unfortunately your best bet is to support the changes and pray that they actually like you for you, which in most cases they do.
In your case, I get the sense that this dude was a serious a-hole to begin with, he probably just submerged it. Your better off without him.
We've all been there. It's so unfair when they love you and leave you like that. But trust me, you're coming out the winner in this one.
I guess start dating someone who isn't raging with personal insecurity (we're human, we all have them. But date someone who isn't so fixated on how HE looks... Fuck thats our job) . My mother always said, ugly people have nothing to lose lol . I have experienced this first hand... And you know what, you are better off. As long as you don't let this get you down your going to come out the winner. See if another female tolerates his bullshit, because trust me old insecurities ALWAYS have a way to come back.
And lastly, make sure that you look beautiful...I think the best revenge is living well and caring for yourself... Never let the ex see you looking tore up!
MM, love the tag.