Had it not been for Madame Bourmdernoot, the sisters Van Cruysen, and Suzette Berger, he would never have known how priceless Felicie Nanteuil was to him.

If one must be literal it may be argued that he was unfaithful to her.

That is the correct expression.

There are others which come to the same thing and which are not such good form.

But if one looks into the matter more closely he had not deceived her.