In The Witch of Blackbird Pond, why does Kit end her relationship with William?

After Kit
is arrested and tried for witchcraft and the charges against her are dropped, William comes to
call at her home. He stayed away during Mercy's illness out of consideration for the family, he
says. Kit is cool toward him because he did not support her during the trial; he didn't even act
as a character witness for her. When Kit shows him out that evening, they have a private
conversation. Although he says he missed her, he makes it clear that he expects her to put her
unpredictable ways...