Going back back back.....gone

One of my best friends is insane. She has gone back to the boyfriend who cheated on her (for months) last year. After hearing all summer about how much better she was than him, about how he was fat, bald, and didn't treat her right, and about how she would never talk to him, she goes back. I just cannot understand this. She is a smart, fun, and kind girl, seemingly competent in all other areas of her life, yet she goes back. What would possess a sane person to do this?

Her concerned and loving friends have tried to stop this. We echo back the complaints we've heard a thousand times, we appeal to reason, faith, vanity, pride. Anything. But nothing works. Now we've become the bad guys, the enemy, and are just driving her closer to him. The usurper. But what else are we to do? Yes, people have to make their own mistakes, but this one should have already been learned! This isn't the first time for her. Going back. Are we so needing of affection, so lonely, that we return to the familiar, no matter the cost? She is not the first or last to jump back in the pool, but she is drowning, and there is nothing we can do to help.