When she realizes that Nigel is having an affair, her first sentiment is satisfaction that she figured it out. Her second is that, despite all the palaver about betrayal, it doesn't feel so terrible.This is pleasing--it demonstrates a certain sophistication. She wonders if his fling might even serve her. In principle, she could leave him without compunction now, though she doesn't wish to. It also frees her from guilt about any infidelities she might wish to engage in. All in all, his affair might prove useful.