In section two of The Sweet Hereafter, why is Billy Ansel turned off by Risa Walker after the accident?

He realizes he shouldn't have had an affair.

She says she had known all along that something bad would happen.

He realizes she wasn't as attractive as he thought.

She gains a lot of weight from the grief.

"The Sweet Hereafter" is actually a story that was written by Russel Banks. And in the second chapter of this story, the reason why Billy Ansel is turned off by Risa Walker after the accident because he realized that he should not have had an affair with her. Risa Walker is actually a married woman. Billy and Risa had this affair for three years already.