This hit me hard and I've been thinking about it a lot. There is no question that my ex has been the person who stressed me out the most by far over the last 2 years; indeed, although our contact is quite limited now, she still is. And I've been thinking about how incredibly incommensurate that is with my fantasies of us having a happy, healthy life together. I realize that this person will always stress me out, and how could I possibly find peace then?
You have a good friend and had an epiphany

Reading the 10 beliefs helped me as well, belief 1, made me realize how true that this person does not hold something over me, I will find someone else.
1) Belief that this person holds the key to your happinessMyth 1 - Belief that this person holds the key to your happiness [Read original text here]
"Idealization is a powerful “drug” – and it came along at a time in your life when you were very receptive to it. In time, you will come to realize that your partner’s idealization of you, no matter how sincere, was a courting ritual and an overstatement of the real emotions at the time. You were special – but not that special."