Hello, I'd like to help you with your question.
It is a normal response to shut down when you feel angry or upset with someone. It is a mechanism to help protect yourself from emotional pain. And the deeper you feel this pain, the more shut down you might be.
People who shut down when faced with emotional upset usually either have a past where they were hurt very deeply by someone through abuse, neglect
or some other trauma, or they tend to be sensitive in nature. Being sensitive is not a bad thing. It actually makes you more in tune to others than many people are, but it also makes it harder to cope with strong emotions. And shutting down is not so much about blame/fault as it is how you cope with confrontations/anger and other emotions.
If you were abused in your past, it could be that feeling very strong emotions through conflict with someone else triggers your feelings from the past. If that is true for you, therapy can help a lot. Talking through your trauma can lessen the pain and help you cope better with strong emotions.
It might also help to develop other ways to cope. For example, when you experience very strong emotions that make you feel like shutting down, try to express your feelings in another way. Journaling or even just jotting down your feelings, talking to someone neutral to the situation or expressing yourself through physical exertion can all help. The idea is to get your feelings out and express them so their impact is less and you can open yourself up again.
If this does not work for you, talking to a therapist might be very helpful. You want to explore why shutting down is your first reaction and what happens when you are confronted with strong emotions. By exploring what causes you to go into yourself, you can understand it better and find new ways to cope.
I hope this has helped you,