What does Dr. Steinbridge realize over the course of Thursday's treatments in the novel, The Wives?

Dr. Steinbridge is the doctor who cares for Thursday when she is in the mental hospital. He is the same doctor who cared for Thursday after her miscarriage and suicide attempt. He cares for her again after she shoots Seth and is sent to the ward as her sentence. Even though Steinbridge believed at first what Seth said about Thursday, he comes to realize that Seth was manipulating Thursday, and that Seth had mental issues of his own.