Killian couldn't stand it when she received even a little hurt. He couldn't stand it when she shed a single drop of tear. Even if it was because of him, he couldn't stand it. However, it was too late to regret anything since he couldn't change the past. He knew Iris hated him and was only tolerating him to survive. Once she was capable of being on her own, he didn't doubt she would leave him once she had the chance.
Then, he would let her go and leave her be. If one day Lord Kieran returns or Iris falls in love again, he would personally hand her over to the person who would bring happiness to her. Unless she asked him the truth, unless she made a choice and chose him, he would let her be.