I'm sorry to hear that you are having some low emotional/mental times. I do think that what has happened is that they have accumulated and are now just hitting you. You've been a busy woman with family, jobs, etc. and it's all caught up with you.
The thoughts of leaving are very normal for us, especially when we have had to carry the load of responsibility and accountability for a long period of time. Are you taking any AD's? If not, this might be something you may need to look into because some of what you are describing may be symptoms of depression.
I am glad to see that your S21 has a full time job and your D19 has gotten a job. This should take some of the worry off your shoulders.
I do hope that your counselor can help you find a way to work with you on helping you climb out of that dark hole.
Please take care of yourself.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.