I've always loved this line: "And there's this burning like there's always been. I've never been so alone and I've never been so alive". Sometimes there's a relief that can come with a break up that you weren't anticipating and it can flood you with a sense of freedom. I've experienced it a couple of times. I've been glad to be rid of someone yet miss them at the same time and then be angry because I miss them. It's the same thing here: "And this is the last time we'll be friends again. I'll get over you. You won't know who I am." I can't tell you how many times I've screamed that line! There have been a couple times, at the end of a long relationship or after living in one place for many years, that I sensed that I'd changed a lot since the beginning but I needed to get away in order to complete the transformation.
This song can probably mean something different to everyone based on their life experiences and I think that's cool. I like that the singer is going through those emotions and phases during the song. Many of Third Eye Blind's songs are like that for me. I enjoy them because they come across as extremely genuine.