Because when a person 你 爱情 lets 你 down, betrays 你 或者 does something unspeakable, it is a thousand times worse than if any old stranger did it because 你 trusted them. And when that trust is chucked back in your face, the worst kind of hatred is born. Emotional damage is some serious stuff :|
I don't per say despise them but I know I don't like who my ex became, it can happen when someone 你 爱情 hurts you, emotionally 或者 physically 或者 both which both was the case with my ex, he was my first 爱情 & we were married for 23 years but after going through that it changes the way 你 feel about someone.
It depends 更多 on the individual situation. I'm not one to believe that 你 can truly hate something 或者 someone that 你 once truly loved and vice versa. However, this is me and I have issues with attachment.