Manslaughter by Alice Duer Miller

Lydia had offered to drop Bobby at the railroad station on her way home, although she had to go a few miles out of her way to do it. He was going back to town. It was dark by the time they started. She liked the feeling of having him there tucked in beside her while she absolutely controlled his destiny for the next half hour. She liked even to take risks with his life, more precious to her at least for the time than any other, in the hope that he would protest, but he never did. He understood his Lydia.

After a few minutes she observed, "I suppose you know Eleanor has a new young man."