Why do we all inevitably resort to using that hackneyed, self-effacing line whenever giving a lover the dump? I think the best case scenario is that it’s to spare the other person’s feelings. Dropping them into the night is hurtful enough, so you hardly need to go into graphic detail over each faux pas, real or imagined, that they ever inflicted on you. (“You used my toothbrush once and lied about it. And you only tip 14%…”) Also, by time you’re ready to go solo, you’re generally so fed up with the person that you feel hashing out every single interpersonal conflict from the past three years—or three weeks—would be a complete waste of time when you can instead just beat your own brow and nobly pretend to take the blame. What’s more, you feel the person will leave much faster if you don’t recriminate them—and this way, they can’t argue with you or try to defend themselves at all. You’ve already said YOU’RE the problem and absolutely there’s no way around that. End of argument.
It’s too bad the line comes off so damned 1940s-weepy-British-romance-drama. You know, “Dahling, please don’t take offense if I dare to utter the suggestion that we should part. After all, it’s not you—oh, no, my angel, you are beyond flawless and the perfect lover in every way—it’s me! I don’t deserve you. I don’t deserve anyone! I’m completely damaged goods and irrevocably unmarriageable!” And then, of course, you go right on to your next marriage. Hey, maybe it IS you!