Are you sure he didn't poo or pee out some urates? Did he shed or anything?
Your snake looks okay to me. It sounds like you're just feeding FT and will be trying live. I'm sure when you offer live he'll be fine.
Have you tried anything besides rats or mice? Some of them like things like chicks and/or quails. I've had a couple on fasts who I offered an FT chick to and it got them going again.
Try something different like a FT chick. Then if that doesn't work, do live for a few months to get him going again and gaining some weight.
I definitely wouldn't rehome him yet. He's not doing terrible at all. You clearly are attached to him, and honestly, you're probably far more frustrated and affected than he is by this.