Most Helpful Girl
To try and make themselves feel better about the awful thing they've just done. There's never an excuse for cheating. It's a horrible thing to do to someone.
Most Helpful Guy
They want to do something deplorable and most people are narcissistic and always imagine themselves as being like the protagonist in film that is morally just and they are looking for a way to warp reality where they can do shitty things but still act as if they are the hero.