It is not your fault that you are put in this situation.
Neither is it your fault that you have been forced into managing the family alone during this season of events.
It is healthy and proper to establish the boundaries of unacceptable behavior, especially abandonment and disrespect.
You sound like you have a good portion of courage, compassion, and wisdom to work with. Those are powerful attributes that will get you and your family through this time.
Your children are of the age that they may demonstrate moments of great support and courage. Take in and acknowledge those moments of their maturity, forgive the moments of their faltering (perhaps lashing out) in their young years, and remember that you are wiser and stronger than you believe or feel you are.
The incident a few weeks ago regarding your husband asleep in the car for an hour.... was he passed out, or did he do that intentionally? How far is his mind running with thoughts of self-destruction? Please, for the sake of all involved, find out the details of that incident, directly but compassionately discuss it with him, and find out if he has any thoughts of intentionally harming himself. If he has a plan to harm himself, please do not hesitate for a second; call 911 immediately and get professionals to intervene.
Again, I encourage you to introduce a professional therapist into this situation, as a therapist trained in this area will make all the difference in your health and the outcome of this situation. All is most definitely not lost.
I echo the well-wishes of the others here. It is quite possible your husband will find his path to healing and will return to being the man who first won your heart.