Hugs. This too shall pass. It sounds like you are doing many of the right things to hold yourself together. Just because your son relapses doesn't mean you have to - into codependency or alcoholism. You know that help is out there. You know what you need to do - just like a cancer patient. No one WANTS to go through miserable chemo and radiation, but they do it anyway. They just buck up and do it for everyone else in their lives. It is not going to hurt you. It will make you better. So I hope you will just TRY to make it to a meeting - try to step outside your depression, outside of yourself and get to the al-anon meeting.
The disease of depression is doing everything in it's power to keep you sick. So you are going to have to fight back by going to that meeting. Good luck. No matter what, you'll get through this - as long as you stay sober. Keep us posted on how things are doing.