WTHeck?

I realize that I'm not exactly a fount of common sense, so there are a lot of things I don't understand... Jason Mraz for example... but how is it that you can know everything about a person and still need them? How can you know that someone is shallow and insecure and totally clueless and still depend on them? How can you let someone so completely untrustworthy have so much of you? You know that you are giving them all the ammunition they need to hurt you, but you still need them? How many times do you need to let the same person hurt you in the same way before enough is enough? How can you love and hate the same person with equal measure? I guess I'm trying to be rational about something irrational. But what adaptive purpose could this phenomena possibly serve? It makes no sense, yet most people experience it.