He wanted to tell him that his cous- not cousin being a half-blood was nothing; that he'd known, held, someone else's same secret for years; that his wife was as well, and for him to be was hardly an issue at all. Saying so, however, would quickly break the truce of giving away such a secret of his wife's; it was not something that was his to share.
Although Cass did bring up a point that he did wonder about. "Alright..." he moved slightly in his chair.