The Shadow of a Man by E.W. Hornung

Moya went to bed like one already in a dream. She smiled when she realised what she was doing; there would be no sleep for her that night. Yet she went through with the empty form, even to putting out the light to rest her aching eyes. And in five minutes her troubles ceased for as many hours; she had passed that pitch of excitement which is another name for insomnia; she had reached the stage of sheer exhaustion, and she reaped the recompense.

Spurred feet treading gingerly nevertheless awoke her towards dawn. It was a bitter awakening. Further sleep was impossible, further rest intolerable; besides, something must be done at once. It was an ordeal to face, but sooner or later Theodore must be told, and then -- good-bye! Obviously the sooner the better, since the thing was settled between the two whom it concerned; and Moya had the temperament which prefers to precipitate the absolutely inevitable; but temperament for once was not her lord. It was too hard!