He knew that she had promised to marry Dare if he were free.

He knew that, having made that promise, she would keep it.
It would be mere sentimental folly on his part to say the word that would set Dare free.

Even if the American woman were not his wife in the eye of the law, she had a moral claim upon him.

The possibility of Ruth's still marrying Dare was too hideous to be thought of.

If her judgment was so entirely perverted by a morbid conscientious fear of following her own inclination that she could actually give Dare that promise, directly after the arrival of the adventuress, Charles would take the decision out of her hands.