I don't know how to express or articulate my thoughts and my vocabulary and grammar gets messed up the more I write so I will just write simply.
What I'm trying to say is that every day or hour or minute or everytime you think, you feels like your original selves is dying. I know that we are constantly growing but i just can't stop thinking that whenever we grow or learning new things or start to think differently, our past selves is dead. I think back to my past selves in middle school, highschool and from 2022 and think, aren't they dead? No matter what i do or think or whatever happens to me, i can't bring back the personalities or "me"s from the past. They remain dead and continue to being dead. Unless they are exist in another timeline or universe.
What exactly is identity, consciousness or the self which is me? I don't know nor understand but this idea just stuck in my mind and occasionally appears when I'm bored, stressed or relaxed.
Some folks apparently consider this depressing, but I found it helpful to accept that I'm just a pile of atoms drifting through the universe.
I'm 'alive' in the medical sense, so there's lightnings going between the piles of atoms within my brain and another pile of atoms continues to wobble in the appropriate way to pump a soup of atoms.
But I'm not alive in a sense that inflates meaning into it, which we do a lot:
Similarly, the past and the future don't exist. They're concepts we've made up. The whole time traveling brouhaha in science fiction might make one think that they exist more concretely, but that nonsense foots on a missinterpretation of Einstein's theories.
So, there's not a meaning to your past self being alive or not. It really is as simple as it just not existing.
And ultimately, without inflating the meaning of being alive, there's nothing to be sad about either. Because, while it's fancy when piles of atoms do the lightnings and the wobbles, it doesn't matter which concrete atoms are part of that fancy pile.
You can even stop thinking about your pile of atoms and rather consider yourself part of the big pile of atoms which is the Earth or the whole universe. That big pile of atoms is quite immortal.