He feels even more screwed over by life when he is told in no short of terms that a Dark Witch will probably try to kill him at some point because of a prophecy. So in preparation, he should go along with learning Magic and to fight her for when the inevitable time came and she would come to kill him. It was not much of a choice, learn to fight to live another day or die sitting in a mansion with people that pretend at best he doesn’t exist and at worse hit him with things.