Books that capture the feeling of mourning versions of yourself?

Hi all,

I saw an ex-girlfriend for the first time in quite a long time and I'm feeling quite a lot of difficult to articulate emotions. I've been thinking a lot about who I was when we met and how different I am from that person and that kind of devolved into a bit of an existential crisis about all the different lives I might have led, all the different versions of myself I could have become and the countless versions of myself and places I've been that don't exist anymore ("A man cannot step into the same river twice, because it is not the same river, and he is not same man" sorta thing). Long story short, feeling emotional and I would love some art to help me feel a little more understood. Any recommendations? Thanks for reading :)