Definitely put the oxygen mask on first. You have been to "go to" person for a long time and have been super strong for your children. They are still young and don't understand what you have been through and are still going through.
Maybe I missed something along the way, but have you thought about putting down in writing how you feel? Sometimes, I would be so out of it, that pen and paper helped me get my thoughts together. You don't have to share them with him unless you want to.
We are always here for you. We do understand what you are going through. Again, I wish that I could give you a hug.
Be kind and gentle to yourself. Take it one day at a time.
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.