Everyone who is in your life right now, everyone who has ever been in your life, and everyone who will ever be in your life in the future is your very best friend.
They were willing to take time away from their explorations of their own lives to invest time, energy and effort into helping you explore your own life. No matter what kind of impact they are having on your life, or what you think about them, they're doing you a huge favor.
They wouldnt be there if you hadnt asked them to be there, the fact is that you/we are attracted to negative states and situations because it allows us to explore our own feelings and understanding. And discover what it is we do want in our lives.
Perhaps you'll find it useful to feel some gratitude from time to time(even if that person has hurt you, or is hurting you now)