LostandBroken, welcome. I am so sorry. It is a hard road you find yourself on, I understand how you feel. I'm sorry that right before this holiday you are in pain and heartbroken over the actions of your son.
At 21 your son is an adult. He is responsible for his choices, regardless of how poor they may be. You cannot control any part of his life. As painful as it is, usually the only choice left to us is to begin to let go, to detach from their choices and their behaviors and learn to live our own lives as well as we can.
You may want to read the article on detachment at the bottom of my post here. It also sounds as if you and your husband might benefit from counseling. Years of this kind of trauma wrecks havoc on marriages and relationships. You will need help to repair that damage.
Many of us have been in your shoes and have learned different ways of responding so that boundaries are set and we can step back from the edge and evaluate what it is we truly want to do next. Not out of guilt or fear, or anger or resentment, or worry or sorrow, we've all been through those emotions.........but to ask ourselves what is it that I want and what is it that I need. You have likely been taking care of your sons needs for a long time and if he has a drug and alcohol problem then you are dealing with the substances, NOT your son. Usually most of us begin to change after we are utterly sick and tired of the way our lives are not working. We hit a wall. We can't see a way out. But sometimes that is exactly what needs to happen to wake us up so that we take a different action.
You won't lose your son by something you did or didn't do, he is making those choices.........he is choosing drugs, alcohol and stealing. He will have to bear the consequences.
Take back control of your life. If your son is moving, there is nothing you can do but to learn to let go, to accept his choices, to accept what you have no control over. It is not easy, but otherwise you will suffer trying to change something you have absolutely no power to change.
Get yourself support. You can likely find some immediate help, particularly around the holiday, at an Al-Anon group, or Narc Anon, or Families Anonymous, many of our parents here find great solace and support in these groups. Private therapy and a parent group helped me. CoDa, another 12 step group is helpful. Continuing to post here will offer you support as well.
You will need to find ways to bring your marriage back to life if it has been attacked by the insanity of troubled young man who has been stealing from you. Step away from the immediate issues and take a look at how you can move ahead now. It is heartbreaking to have a troubled child who won't seek the help they need, who behave in ugly and hurtful ways towards us and use our love for them to harm us........at some point though, we need to be the ones who change, we need to realize that our lives are worth saving, worth finding ways to bring our joy and our peace and our aliveness back. You deserve to have a life which is separate from the negative choices your son is making. You deserve to feel joy and pleasure and to have peace of mind. You can choose joy and peace. You can let go of what you can't control. You can move through this and come out the other side feeling good about yourself. I know this because I've done it. As have other parents here.........we've struggled like you are and we changed. So can you.
Hang in there and get yourself some support. Keep coming back. We're here.