I think that it means this:
Hello, how you doing?
What's it like to ruin all my self-esteem?
Let me blow off some steam
For five years I waited, so why am I jaded to get back at you?
What it makes it cool
SHE LEFT HIM, AND HE STILLLOVING HER, AND HE HAS WAITED FOR 5 YEARS
When you act like nothing ever happened
I feel like I should feel bad
But I can't like someone who thought they're the only one that mattered
I hope that you're flattered
'Cause you broke this down
The best thing that you never had
SHE SEES HIM AND SHE ACTS LIKE NOTHING HAPPENED, LIKE THEY NEVER KNEW EACH OTHER, SHE THOUGHT SHE WAS THE ONLY ONE AND SHE WAS VERY SELFISH AND SHE DESTROY THE REALTIONSHIP BUT HE WAS THE BEST THAT EVER HAPPENED TO HER AND HE LOVES HER
I think that it means this: Hello, how you doing? What's it like to ruin all my self-esteem? Let me blow off some steam For five years I waited, so why am I jaded to get back at you? What it makes it cool SHE LEFT HIM, AND HE STILLLOVING HER, AND HE HAS WAITED FOR 5 YEARS
When you act like nothing ever happened I feel like I should feel bad But I can't like someone who thought they're the only one that mattered I hope that you're flattered 'Cause you broke this down The best thing that you never had SHE SEES HIM AND SHE ACTS LIKE NOTHING HAPPENED, LIKE THEY NEVER KNEW EACH OTHER, SHE THOUGHT SHE WAS THE ONLY ONE AND SHE WAS VERY SELFISH AND SHE DESTROY THE REALTIONSHIP BUT HE WAS THE BEST THAT EVER HAPPENED TO HER AND HE LOVES HER