Tad, I am very sorry to hear about your mother. Spend as much time as you can w/her. Take some photos of her so that you will have them to look back on the days, years to come.
You don't have to be your xw's friend, but you can choose to be civil. She still doesn't get it and most likely never will or it will be a long time from now. She may feel a little remorse, but she will never admit it and you shouldn't put your life on hold for her. Tad, she has moved on and no matter how hard you look, she's not moved very much in her crisis. She's still playing out in left field and life is moving on each and every day and your life and your sons' lives are moving further and further away from her.
Tad, focus on your mother now...it is very important that you do so. You don't want to have any regrets after she has left this world.
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.