. Now I can barely get a smile or "I love you" with his cold, empty stare. How does addiction change people so much and so rapidly?
One of things I learned is that even when they are clean/sober the disease doesn't stop. When they relapse, they are exactly where they were before they got clean.
Addiction lives in the same part of the brain that tells them to breath. He will do and say what ever he has to do in order to get the next high.
Why are you driving him to work? Does he not drive? Has he lost his license?
Its very important that you NOT believe his words only his actions. I would strongly suggest that you not allow him back into your home, change the locks and protect yourself and your finances. Be lucky at this point it's only $500.00 you've lost because it can will be so much more if you allow him back any time soon.