For me it's about rebounding. He's hating her but remembering the good times, and then loving her, and then remembering the pain and the reasons they broke up so hating her again. At the end he resolves and says that the bad parts about her will remain forever and then concludes 'it's so good to be in love again', because he's temporarily found a way to keep the feeling of being in love but with someone who doesn't have all those bad parts - a new rebound girl.
For me it's about rebounding. He's hating her but remembering the good times, and then loving her, and then remembering the pain and the reasons they broke up so hating her again. At the end he resolves and says that the bad parts about her will remain forever and then concludes 'it's so good to be in love again', because he's temporarily found a way to keep the feeling of being in love but with someone who doesn't have all those bad parts - a new rebound girl.