I am SA with some FA traits that only emerge I have learned, when paired with a DA. I would say that I recognize in my ex the pattern you describe with the shutting off and using the experience as reinforcement and validation of childhood trauma. I would also say that in my experience, remaining friends - or trying to anyway - when someone is shut off like this and won't have candid conversations about critical past issues surrounding things like care and trust, is extremely difficult to achieve if not outright impossible. You are right that you will have to effectively coddle him around all of this while simultaneously not having any mechanism for mutually rebuilding trust, because he won't talk about the things that are critical to building trust which is a core component of friendship. Largely you have to swallow all the burden here of effort in trying to rebuild anything when really the responsibility should be on him. All that along with the threat that if anything goes wrong, he will likely retreat into more trauma self validation.

You can't build a healthy friendship with someone if you have to behave like you are their therapist.