eX's and O's

So the other day I was talking to my friend Micail at work about ex boyfriends. We decided that the whole concept is so backwards. We spend all this time getting to know someone, and letting them really see who we are, and then just because we decide they're not the person we want to spend the rest of our lives with we just quit. Quit the relationship, quit the friendship, and quit everything that we've worked towards. These so called "ex's" should be out closest group of friends, and our go to people. I'm not saying that we should call them up every Friday night, but when we're having a rough day, or just need someone to talk to, they should be there. How come instead we just ignore and avoid? How can you go from spending 24/7 with someone to never even talking. These people know us on a more intimate level then most people, they understand how we work and think. How did breakup come to mean erase from life?