Well I don't think he LOVE loves both of them. On one hand he has the faithful trusting girlfriend. I'm sure he loved her at some point, but I think he's started to feel it's just not the Fireworks kind of love anymore. So there's the OTHER girl, he's been seeing her, and has probably fallen in love with her, but he realizes that his girlfriend has always been there for him, and is a good person, and she doesn't deserve to be cheated on, so he makes the decision to stop cheating on her, and leave the new girl even though he loves her.
Well I don't think he LOVE loves both of them. On one hand he has the faithful trusting girlfriend. I'm sure he loved her at some point, but I think he's started to feel it's just not the Fireworks kind of love anymore. So there's the OTHER girl, he's been seeing her, and has probably fallen in love with her, but he realizes that his girlfriend has always been there for him, and is a good person, and she doesn't deserve to be cheated on, so he makes the decision to stop cheating on her, and leave the new girl even though he loves her.