>>when you die, you are dead for eternity and what has composed you will never exist in the same composition ever again.
Yeah, so? What does "you" even mean anyway? Most people who ask this question have never really thought about it with any kind of depth or honesty.
Bill Nye taught you in elementary school that all your cells die and are replaced every seven years. So it's not the physical substances that make you "you".
Is it the pattern in your brain? Maybe, but even that's doubtful, given how much people can change over just a few years-- And I'd take it even further. In a lot of ways, you aren't the same person from one moment to the next.
All the time you're possessed by different personalities. They awaken, and then drive "you" to some goal. They feed you motivation, they give you a drive, push you to do certain things. Sometimes things you know you shouldn't do.
Think back. When was the last time you were really conflicted about something? Like half of you wanted to do something, maybe something awful, and the other half was afraid of the consequences that it would bring about? Conflicting drives. Those things have their own desires, and they're only partially under your control, but they're just as much you as the part that whispers "I" to yourself.
In fact, you can barely say you have control over yourself at all if you don't have these conflicting drives. I mean, how else can you say you've made a choice when there wasn't some part of you that would have gladly done the opposite?
You've lost your innocence. I get it. The presumptions you had since you were a child no longer hold, and you want someone to tell you something that will let you put them back, but it's hopeless. Humpty Dumpty can't be put back together again, you can't go back to the womb. The only way out is forward.
Embrace the mystery. Cultivate that uncanny feeling, and plumb the infinite.