He says, "since I broke up with What's His Face / I'm a different man," which illustrates how scarred and heartbroken their breakup left him. He's a completely different person than before, so how can we keep him true to our previous standards? How can we expect him to be the decent man he apparently was before if his heart was so badly broken? Physically he cannot be that person. We cannot hold him to the standards we hold everyone else to: he is heartbroken and deserves our pity rather than ours.