I agree with Annabellemore.
To me, the degree to which people are honest or not honest defines their basic character. And if somebody is lying to one person about something so important, I just assume they are or will lie to me about important things as well.
And frankly I have not a lick of patience with dishonesty. It's cowardice. He can rationalize it all he wants to make himself feel better about why he's lying, but he's deceiving himself, and her.