Ethan didn't doubt that Norah loved him, exactly.  He was a fair judge of character, and could see in her eyes, and kisses, and silent movements, a love that would be very difficult to fake.  He also knew well that she was not a person who would bother to fake any of those things anyway. But she didn't love him the way he loved her.  Of this he was equally sure. 

Ethan loved Norah in a way that had become inextricable from his very body.  It wasn't just that he loved her, but that he loved nothing but her.  To stop loving her would be possible only through the reordering of his entire spirit.  The way Norah loved was just as real, and one could even say just as strong.  But her love worked like an intricate and complex program, one that had taken Ethan as input and produced love as the result of a series of calculations.

Ethan was reassured by this on one level.  Norah had not fallen in love with him as the result of fate, or passion,or  being struck with a magic arrow .  She had chosen him, and it is a marvelous feeling to be chosen.  On another level, Ethan was terrified by this truth.  If she had chosen him, it was theoretically possible that she could unchoose him.  Whether she ever used it or not, Norah's love had an off switch.  The program that had selected Ethan could someday be deleted.  Ethan's love could not be deleted.  It was his operating system, and the removal of it would cause a complete system crash.

~

To her credit, Norah also knew this about herself, and didn't like it.  She didn't like the fact that she had never been in love, not with Ethan, and not before him.  She had loved, fiercely, passionately, even foolishly, but that was not the same as being in.  She was very careful not to let this become an advantage.  A lesser human, upon recognizing that she or he was in a position of power over another, would use that fact to win arguments, to stack up little victories, or otherwise to secure territory.  Norah saw chances to do this all the time, and never once took the opportunity.  She was terrified of becoming one of those women who plays with hearts like figurines, and who is interested in getting what she wants out of a relationship.  Norah wanted nothing out of her relationships.  The relationship itself was what she wanted. 

If anything, she worked harder at the relationship than Ethan.  She yielded in countless little ways to his whims, far more than one might say was her share.  She worked harder than she needed to to make him happy, partly out of a sense of fair play, but partly because it made her feel human.  She knew that she could win any argument with a cold glance, simply letting her hand hover over the off switch for a moment.  For that reason she always yielded.  To win that way would introduce an element of threat into the foundation of the relationship, and it would cease to be love.  It would be blackmail.

For Norah, Ethan was a good man, who loved her deeply, and who also happened to be attractive, interesting, and kind.  And so she loved him.  For Ethan, Norah was a cold and terrifying magic that he had no choice but to love.