When you are in love with somebody, you are blind to all of their flaws. Their flaws, to you, are technically what makes them perfect. So that's why whenever you break up with this person, you begin to see all of their flaws that you didn't realize he/she had whenever you guys were together. And that's why typically after a breakup, especially after a bad breakup, the two sometimes may not want to see each other again, because the love has turned into hate. The reason that you may begin to hate this person, is because it's your heart's (technically your brain) way of getting over that person. For example; A guy dates a whiney girl, who at the time of dating her doesn't consciously realize she's actually that whiney, only sees her whininess as a form of attraction, because when he's in love with her, there is nothing in particular about this girl that he can hate. But when something goes wrong in their relationship that causes them to separate or breakup, bad especially, he becomes conscious of all the flaws that he once saw in her as "attraction". This initial state of "attraction" turns into "hatred" and he begins to question what he saw in this girl. It's human nature.
So it's been said that everything happens for a reason in life. Life is a puzzle that we create. The pieces that we put together in our puzzle are known as choices. Life is probably, if not is, the only puzzle to where you can connect the pieces however you want to and it still fits. But, all the pieces that have been put together are incapable of being removed, hence the saying; "Make wise decisions, because you can't take back what has already been done". Everything DOES happen for a reason, and i'm going to prove that. Let's take it back at the day we were born, where we are impotent in consciously remembering things. Our brain is very unique. The people that we saw when we were an infant, are potentially in our dreams. Because when we dream, every person that we see is someone that we may have consciously or subconsciously seen sometime in our life, for instance; when we go out in public and we set eyes on other people, whether consciously or subconsciously, our brain saves those images. Anyways, back to the main topic, the people that we meet and befriend in life, all add up to the person that we are today. The people who disappear and we never see again in our lives, have already done their purpose in our life. Good or bad.