I rarely post, for reasons I have explained in another post.
I have followed your story. I may be harsher than the others, but I do mean it in good spirit, so please don't take offense.
You are expecting too much. Your son is telling you that he is not emotionally invested in his treatment. If he were emotionally invested he would not be asking you to "bring him home." He would accept that he is where he needs to be.
I know that you feel that you are practicing detachment and setting boundaries, but, truth is, you are way too involved in his addiction.
You picked out a program that you thought was right for him. The reason he stays is because he has no choice. He has nowhere to go and no way to get there. He is away from you, he is away from the enabling girlfriend, and away from the system he knows in Florida. He is biding his time, if you will. It is like being in jail. You don't want to be there, you just know that you have to toe the line and go with the program if you want to get out. Addicts don't get sober until they decide they want to get sober. No amount of "forcing" them into a program ever works.
Remember, your son is an addict. Addicts are manipulative. They know how to say what people want to hear, and he knows what you want to hear.
Your son sounds like he is emotionally immature. He is dependent on other people to make his way in the world. You, then his girlfriend. He doesn't seem willing to stand on his own 2 feet. Even they way he phrases it, "are you going to bring me home?" sounds like a kid away at summer camp who isn't having a good time. It will not help him to encourage this behavior by allowing him to live with you. Realistically, at 22 a lot of us were out on our own, some of us raising children and running a household, in addition to being employed.
Please listen to what the others have said. Even if your son does turn it around and become invested in his program, allowing him to live with and be dependent upon you will not be healthy for either of you, and may well trigger a relapse in him.
Sobriety is not just about not using, it is about changing your whole life. Changing all those old bad habits and ways that keep you stuck where you are in life. People, places, and, things. This is what they teach in AA/NA. These are the things you must change. When you have an addict in the family the whole family is sick, not just the addict, and the whole family must change.
Think of it like going on a diet. You can go on a crash diet and exercise 4 hours a day and lose the extra weight, but after the weight is gone if you go back to the same old overeating, sedentary lifestyle, you will gain the weight back.
Very few addicts make it without a support system. I think it is unfair to drill into an addict's head that all they are missing is religion. If that were so every non-christian would be an addict and no christians would ever be addicts. Is your son even on board with the whole church thing? Does he share your religious beliefs? It is my experience that you cannot force religion on a person. It is something they embrace on their own. Addiction is a complex mixture of psychology, behavior, and genetics. There is no one simple answer to sobriety, but addicts need the support of other addicts. People who have walked in their shoes, who have faced the obstacles they have faced and have overcome them. To suggest that addiction is a spiritual failure on the part of the addict is setting them up for failure.
Emotional development stops at the age addiction begins. "Bringing him home" will not help him gain emotional maturity of accept responsibility for his behavior. It will not help him make the necessary changes that he needs to make to become sober. It is, probably, too soon to discuss this with him, because his main aim in completing this program seems to be to achieve his goal of being dependent on you, and, if you really think about it, controlling your life. Think very hard about how it will affect you emotionally with him living in your home. Let go of all the dreams you have of him walking out of this program and being a new man and think of how your life was when he was in your house before. Is this a way of life you want to live? Remember, the people that can most easily manipulate us are our loved ones. They know your triggers, they know what you want to hear, they know what buttons to push.
Have you considered becoming involved in NarcAnon? There is a wealth of wisdom there.
Good luck.