Walk away and give yourself time to cool off before approaching him/subject. Panicking helps no one and its hard to communicate feelings when your in a dozy.

When you let him engage you, you are letting the situation escalate which hinders either of your ability to speak rationally.

Instead practice leaving the room and use crisis skills learned in therapy to calm yourself down. Teach boyfriend these skills. Once both of you two feel safe, broach the topic once again. The most important part is creating and practicing boundaries. I was like this for a long time but creating boundaries and practicing them saved my relationship.