The Painted Veil by William Somerset Maugham

Of course it was not certain yet that Walter knew the truth, and if he didn't it was better perhaps to leave well alone; but if he did, well, in the end it would be the best thing for all of them. At first she had been, if not satisfied, at least resigned to seeing Charlie only by stealth; but time had increased her passion and for some while now she had been increasingly impatient of the obstacles which prevented them from being always together. He had told her so often that he cursed his position which forced him to be so discreet, the ties which bound him, and the ties which bound her: how marvellous it would have been, he said, if they were both free! She saw his point of view; no one wanted a scandal, and of course it required a good deal of thinking over before you changed the course of your life; but if freedom were thrust upon them, ah, then, how simple everything would be!

It was not as though any one would suffer very much. She knew exactly what his relations were with his wife. She was a cold woman and there had been no love between them for years. It was habit that held them together, convenience, and of course the children. It was easier for Charlie than for her: Walter loved her; but after all, he was absorbed in his work; and a man always had his club; he might be upset at first, but he would get over it; there was no reason why he should not marry somebody else. Charlie had told her that he could not make out how she came to throw herself away on Walter Fane.