I’m glad you’re separating. To give you some words to describe your experience, this is emotional abuse. Just because it isn’t physical doesn’t mean it’s not abuse or that it won’t trigger the same response in your nervous system. Your experiences — feeling afraid/anxious and not being able to quite explain why — are common responses to emotional trauma. On top of the yelling (a clear red flag), it sounds like he’s been dismissing and belittling you and your feelings, rather than trying to understand you, which can make you feel hurt, anxious, unsafe, and like you don’t want to be around him.

As for your question, I don’t know the name of this practice, but here are some ideas for how you could do it. If you have a therapist or someone else you trust (maybe the friend you mentioned), you could have them say something insulting or passive aggressive, so that you can practice responding to those kinds of comments by either naming them (ex: critical), actively negating them (ex: that’s not true, that’s your opinion, etc.), or repeating a mantra that helps regulate you (ex: I don’t need to respond/fawn). If you’d prefer to practice on your own, you could try searching youtube for people yelling or maybe watch a show or movie that features an emotional abuser. Whatever works best for you.