He went from a supporting figure to a sudden turn on dime telling me I was selfish, I'll quit everything I'll ever do in life, including my children, and after I finally gave up on defending myself i broke down so hard that I physically couldn't do anything but sob into hyperventilation for ten minutes as he sat not three feet away and acted if I wasn't there.
This sounds totally humiliating, not life-threatening (I think that's the response you are bumping into, and some of the confusion here). None of that makes his actions right or okay. But hopefully your therapist is helping you get to the bottom of how negatively this kind of interaction has affected you.