Don't grieve alone; 14,000 members and growing
I am not married at all, but I lost my Mother in April to a five-year battle with vascular dementia.
I do not know anything about being married, much less unhappily married. However, I can tell you that my mom's lost hurts more now than it did in April. I buried her on the 17th of July, months after she died, because of the pandemic not allowing funerals up to that point.
Despite the fact that we have different marital statuses, perhaps we have something in common in that we are both going through the losses of our mothers alone. It is not easy, it is very painful.
Personally, I go on because there are other people who would be devastated if something happened to me. I also try to exercise as much as I can, since exercise releases endorphins and endorphins make you feel good.
My heart and thoughts go out to you.
I am not in your situation, but since you have had basically two significant losses (the death of your mother, and the death of a happy marriage), it might be helpful for you to consider seeing a therapist. At the very least, it will give you a safe place to vent and maybe rage, whatever you need to do.