As to the other question of his giving up Lucia, Maurice never troubled himself to think about it.

He was, it must be confessed, of a singularly obstinate disposition, and in spite of his legal training not particularly inclined to listen to reason.

Knowing therefore perfectly well, that he had made up his mind to marry Lucia, provided she did not deliberately prefer somebody else, he felt it useless to complicate his already confused ideas any further, by taking into consideration the expediency of such a connection.

There was quite enough to worry him without that; and by some inconceivable stupidity it never entered his head that, while he was really so completely incapable of altering his mind, other people should seriously think he was doing it.
Yet as he read Mrs.Costello's letter over a second time, he began to perceive something in its tone which seemed to say clearly--"Don't flatter yourself that the matter rests at all with you.

I have decided.
I am no longer your ally, but your opponent." At this a new element came into play--anger.
He had been rather unreasonable before--now he became utterly so.