Familiarity breeds contempt.What do you think? Actually, sometimes, the time that you spend with someone doesn't matter if you really want to know them. You may be friends with someone for 10 years and yet, not know every single detail about their life. It all depends on a person, really, if they want to open up to you and tell you their darkest secrets. Or if they trust you enough. This is also applicable to a family member that you have known for years and been close to. You have known them for a long time and accepted their imperfections, and these might annoy you, but hey, they are your family after all. And to someone you have known for so long, you treat them as family.
How do you know if at one point in your life, you become disdainful of one person because of his or her actions and character? And this hatred that you feel might go away, or be repressed, because you will feel guilty about it, but sooner or later they will show their true selves once again. Would your hatred resurface? And once you see this person's faults, you judge them on what they do. You may ask for forgiveness, for you don't really want to experience this cold feeling especially if you treasure this person. And also, you have known this person very well for a long time, you've seen their true colours, and yet, sometimes, you just can't help but despise them. Which you sincerely hope would vanish someday.
It's quite amazing and scary on how relationships work. When a person makes a mistake, different feelings arise. The emotions are jumbled all together, confusing one's self on what to show and hide. But it all depends on a person, really, on how they handle it. It's either they make it work and last long (accepting the flaws and all), or end it before a huge conflict happens. But most of all, we have to learn to forgive. That way, the repressed feelings of hatred and contempt would soon fade. It may take long, but at least, effort has been made on your part.