There is relief from some grief this way, tt.
When relationships are simple and built of mutual kindnesses (like my MIL)... the origins AND the Why are the same answer - we love and care, and feel that opportunities for this mutual relationship are at an end, with death. For me, the kindnesses and caring continue from that relationship in memory - along with a steadily decreasing sadness of parting; echoes. Instead, I think I build altars - light candles - in my mind, honoring the simple goodness of those kind of relationships; and I cherish those memories and try to keep the "goodness" alive.
When the relationships are tortured, complex and even toxic - the grief is different, too. Maybe we could call it toxic grief... because it's a grief that continues on & on... simply because it's grieving what DIDN'T exist, instead of what did. Lost opportunities for mutuality of caring and kindness... sharing... connection... that do not, maybe can not, be created or rectified or replaced. I find my only option is to accept the deficit - the hole where a relationship should be - for what it is... and then try to adjust my mental understanding and expectations accordingly. The mutuality of caring, I can and do find frequently with other people. Why should I let myself obsess on this one? This is my "pep talk" to myself; you know that's still something I have to work on, daily. I am still vulnerable to the latest "outrage", any poke into that old wound...
... I am changing how I respond (or don't) to those incidents. Since I can't change them... I can change "me", enough, that I suffer less and avoid disappointment of expectations by simply accepting that the FOO is the way they are; it's a fact that there is no relationship no matter how much I might "care" and want them to care back; ain't gonna happen. Twiggy showed amazing insight at 12, when she realized that she was an orphan with living parents. She might not've been prepared for her bro to prove so hostile too... but I think she's recovering from that disappointment, now.
Anyway... this kind of grief lasts longer; it's echoes are more like a banshee wailing in the midst of a terrible storm - it IS torture; and I'm coming to the conclusion that it's self-inflicted because I'm just too stubborn and hard-headed and persistently hopeful that "this time" might be different; this time a miracle might happen. Is that naive? Foolish? Maybe. I have learned to protect myself better with things like "probability", "liklihood", and lowering my expectations. Why won't I just let go my hope? Because I am a caring person; people do have a change of heart; and miracles do happen. How did GS's house survive the tornado, when so many others didn't? Flat out miracle - that statistical anomaly of life; it happens - not often, but it does happen.
So I endure the ongoing grief, because it's the yin to the yang of caring and the non-existent reciprocity of the caring. When I'm ready to stop caring, I suppose the grief will diminish a lot, too. No idea when that'll happen though! And I'm sure there's still something I'm missing here... I too, can be a "know it all" and I have a long list of griefs... going back before Twiggy's time even. I do accept that there's always something I don't think of or know about... so maybe the "know it all" tag isn't quite the same as someone who's ALWAYS right - no matter what evidence is shown to the contrary. I admit when I'm wrong, too!
Long answer to short question again, tt... seems I still have a lot trying to get said. Sorry P! Back to your topic!
