So sorry to hear of the passing of another person in your life. I've lost my share, young, old and in between, human and four footed, expected and totally out of the blue. As we get older, there will be more and more loss and eventually our own loss. My therapist once told me that part of the depression and anxiety caused by the death of a loved one is the insidious realization of our own mortality. Maybe so.
He also said that one way of coping with that was a belief system that included the possibility of a life beyond this one. You don't have to believe in any one teaching, you may not believe anything in detail, all you really need is to accept the possibility of an existence after this one, and it can help ease the pain. As you go on, you can read what different systems believe about life after this one and make some choices about what you want to believe--choices that give you comfort.
Me? After much research, reading, thinking, I've chosen to believe that there is an d istence after this one, that I will see the people I care for again although we may be very different, and that happiness is attainable in that place if not here. It comforts me, helps me get on with my life and the grieving process, and reduced the pain. The best news is: If I'm wrong, I'll never know it! So I put that as a win all the way!
Have you given any thought to what you want to believe about what's after this life? Does it give you any measure of comfort? If not, maybe it's time to choose differently?
Now any case I am very sorry you're feeling this pain and I'm sending you thoughts of comfort and peace