This may be slightly off topic, but it really resonated with me how you expanded on the definition of grief. I think a lot of people associate it mostly or solely with death.
But grief, I think, is a very useful concept that can be very helpful in making sense of our emotions in hard moments in life.
I was told this by a therapist when I was feeling shitty after my girlfriend broke up with me, and it was quite enlightening to get this new perspective.
I think grief can be basically felt as the result of any loss. Be it loss of a loved one, breakup (loss) of a relationship, loss of your job, loss of a piece of your life.
I'm not sure if I can completely describe this, but I have many times felt some level of grief at the loss of a what-if, a potential future. I make a choice (or someone else makes a choice) and some small part of my future feels closed off. It's a relatively small grief and doesn't compare to losing a loved one or a relationship, or even a job, but I don't feel I have a clear way to address it.
I have found that feeling described best in the Either/Or of Kierkegaard. The chapter called The Unhappiest Man.
Putting aside the dramatic overtone of the piece, the temporal logic, or rather dialectical swoon of the one that is living in the future/pas(t)ivity is very poignant to me.
I think grief can be basically felt as the result of any loss. Be it loss of a loved one, breakup (loss) of a relationship, loss of your job, loss of a piece of your life.