As within, so without. If you hold onto conflict-ridden relationships in your life, the real cause is your inner attachment to conflict-ridden thoughts. When you alter the mental relationships within your own mind, your physical world will change to reflect it. So if you kick negative thoughts out of your head, you will find yourself simultaneously kicking negative people out of your life.
There is a wonderful rainbow at the end of this process of letting go, however. And that is that when you resolve conflicts in your consciousness that cause certain relationships to weaken, you simultaneously attract new relationships that resonate with your expanded level of consciousness.