Also know that the profound sadness you might be feeling is necessary. I find that an intense/deep sense of gratitude and a profound sadness can often be different sides of the same coin.
Try to channel the gratitude rather than the sadness, but know that it's difficult and also know that time is on your side. Over time, hopefully it is the gratitude that wins out. It will, because it always does.
It took a couple of these kind of situations before I was able to reconcile the above (Grandpa passing away, other close family passing away too young, etc)
Good luck, stranger. I don't know you, but I'm human so I get it.
I wish for all the strengths to you to overcome this. Maybe thinking about good life moments of that person could provide some much needed positivity.