Why is it so hard to lose a friend that treated you badly and always disrespects you all the time and she was always saying she is better than you and you heritage is bad when its not?

We would have to guess that you were getting something from the relationship that you do not want to acknowledge. Ask yourself, "what was in it for me." When you can answer that, you will know why it is hard to let go.

Can it be that you are most comfortable in that sort of situation? What were your parents like? Did they abuse you verbally and or emotionally, talk you down, etc.?

In relationships, there is always a payoff. BTW: that person was not a friend. Friends do not treat their friends that way.