Not only intimate relationships, but all relationships are a mirror, reflecting back to us the parts of our psyche that remain unhealed.
If you pay close attention to your internal state during relationship with others, you have an opportunity to see what lies within yourself, and give possibility to the healing of these triggers.
Relationship will always show us the parts of ourselves that remain unhealed. They will always show us where our buttons are still hiding.
Here is a story of a Monk who was meditating in a cave, he reached "pure awareness", or a state also known as the awakened state or enlightenment. He then left the cave and returned to his home in the village, remaining in this state of pure presence as he walked home, with a feeling of Oneness and deep intimacy with everything and all of life.
As he reached what was previously his home, where his wife lived, he saw his wife through the window. She spotted him also. She went to the door and asked him where he has been, why he had left? She was angry with him for leaving her. Instantly, he felt uneasy, the need to defend himself returned, and the state of "pure awareness" appeared to collapse, and he instantly fell back into the state of separation, of past and future, of ego.
Relationship will do this, it will trigger our peace, it will pull us out of presence, it will bring up anger, pain, hurt, all the uncomfortable feelings we so desperately want to avoid.
If we can take the perspective that it is not actually the other person that is the problem, but our own projections, then we can turn our attention inward, by breathing with the energetic quality of emotion, we can allow that energy to move and heal itself. Instead of trying to be "free from" these feelings, we can free these feelings themselves. They are there own energy looking for liberation.
Be grateful for those that trigger you, be grateful for those that show you your pain and your shadows. And use relationship as a catalyst for growth, for liberation, and for freedom.