Who Made the Hearts of the Post-90s Flutter?

I really like a line I came across online: My leaving is only your regret, while your betrayal is merely a step on my path to maturity. Inspired by that line, I felt like writing this short story. I couldn't think of a title, so I borrowed this little artsy phrase... My writing isn't very good, and I don't even know what I'm trying to say. Just read it as a little story~ Theme: