There is no perfect answer for this. Philosophers have been seeking to answer this since the beginning of time and we will all continue to do so until the end of time.

Personally, I try to make a regular habit of thinking about my mortality. Visualizing my friends and family after I'm gone, and seeing how the world keeps on ticking. It helps me limit my own self-importance in the world but also helps free my mind to focus on the things I really care about.

Like you, I would love to be able to many lifetimes where I get to try all those other paths in the road I didn't end up taking. And perhaps we will, maybe reincarnation is a thing. Or maybe the birth and death of the universe is cyclical and we get to try this all over and over. Sadly we can never know this.

If you haven't seen the show "The Good Place", it has some interesting takes on mortality and what it would be like to live forever.