In this story so far, Sethe did not know why Halle did not comply with her in leaving Sweet Home. Later on, we see Paul D comes into the picture and ends up staying with Sethe. In an argument about Paul D pressing Beloved for information about how and where she came from, Halle’s name comes up. Paul D ends up telling the truth about Halle, filling up the mystery that Sethe was trying to figure out. So we see that Halle, actually witnessed what happened to Sethe and how instead of intervening, his heart was shattered and like, his entire psyche was broken. Who else wouldn’t be heart-broken of seeing their wife being treated like that, the schoolteacher stealing her milk must have been the worst that had him shut out and not being able to go escape with Sethe. Afterwards, Paul D saw him sitting ‘blankly’ by a butter churn. He had smeared butter all over his face. At the time, Paul D was ignorant of the events in the barn and thus wondered what had caused this breakdown in Halle. But Paul D could not physically form the words to ask him because he had an iron bit in his mouth. At first, Sethe was mad that Halle did not intervene but that’s when Paul D explained to her.
It is always tragic to witness someone you love being raped, being treated like that. In this case, he was really broken down to the point that he could not even escape out of there with Sethe, leaving her while she goes alone, pregnant. Also, on her part, she did not know the actual truth, making her resent Halle these past eighteen years that she has been away. I believe it was good that Paul D filled in the blanks about the past and set them right.