Gottman's book describes the physiology of men doing stonewalling in arguments (women can do it too). It refers to how things have gone very negative to the point that all the emotions of the stonewaller have to be walled off, and so yes it's part of the four horsemen - Criticism, Contempt, Defensiveness, and Stonewalling. Or maybe your ex is just selfish and just doesn't want to bother with talking to you, instead of being overwhelmed and flooded by emotion.

I do wish you luck in resolving the issue with him! Maybe talk to him through a third party? I don't know your situation though.