I have been in that situation. My RABF's drug of choice was pain killers. He started with a real reason to take them (a broken bone), but stayed on them because he liked the feeling. He had several reasons for "liking" them, but it eventually led to an addiction. As he got more and more addicted, I got more and more sepated from my friends. I was in denial about his drug problem. He would say one thing and act another way. I would try to hide things from friends. I wouldn't admit to myself that he had a problem. I would try to control his usage. All of this lead to me being very anxious and depressed. I'm not saying it was the only cause, but it sure didn't help.
My RABF also lied about his usage and illegally obtained drugs (doctor and pharmacy shopping). He was a different person on the drugs. He became only interested in getting more drugs. He became distant. He was with me, but not really here mentally.
I would suggest that you work on taking care of yourself. There are things you can do like exercise and meditation that may help. It also may help if you can get out with your friends just a little bit. Maybe, just have a short lunch with one of them?
Did you say you were receiving treatment for the anxiety/depression? If so, that is very good. I feel for you, because I've been there.
You might want to distance yourself during his recovery. You don't have to be there for him or give him a second chance. If he decides to get clean, it will be for himself. He has to do the work himself. Meanwhile, his emotions might be up and down, and you will probably be in store for more of his lies.
It sounds like a little much with you taking care of his finances. He is an adult, right? I would draw a line before that point. Plus, the fact that he took money from you is very discouraging.