Here's some more writing from the Stoic philosopher Seneca. In this letter he writes to his friend Lucilius on the nature of virtue and how it can be a refuge from worldly troubles. It's too long to post here in text form, but the link is worth reading. It contains wisdom that's just as profound today as it was when it was first written nearly 2000 years ago.
https://www.lettersfromastoic.net/letter-74-on-virtue-as-a-refuge-from-worldly-distractions/
Well, both figures are documented in history with their existence and relationship confirmed by multiple sources.
Seneca spoke highly of love and was married. His wife loved him so much that when he was ordered to kill himself she wanted to join him.
As far as why someone would keep the letters and pass them down, that's how knowledge and wisdom was handled back then. There was no mass production of books and literature yet available so things were passed around, copied, and also kept alive through oral tradition.
Even if these were somehow fake, what would be the point? Even if Seneca was a fake person and never actually existed it doesn't change the wisdom of the words being attributed to him.