Wow I love this song atm.
Really [this is most likely wrong] but the meaning of this song it that.
The girl hes singing about is cheating on him, but to his face. And like his mates are saying "is that your girl" and he jsut goes "that bitch aint a part of me". And in the video he replays the flashbacks he had with that girl, making out shes just a tease - not to be taken seriously.
Also it maybe that one of the girls Chris is singing about has emotional problems or very complex ones due to the line:
"I want the girl but not what she's going through"
And well I've just comes out a relationship where I've been lied to, so I find this quite theraputic: D