One of the ideas my Pop explained to me as a young boy was that our mouths get us in the most trouble in our lives. A counselor in junior high school once explained to me as well, that it is not what we say, as much as how we say it. Combining those two, I have found that when it comes to having a conversation with someone that creates stress in our lives to use the acronym HALT. Never start a conversation that can become stressful while Hungry, Angry, Lonely, Tired.
If that person contacts you before you are ready, simply say you will call them back and maintain your integrity and sanity. Leaning to say “no” to oneself and others is a real challenge of maturity.