Oliver smiled at her a bit, the look he wore entirely self-effacing. He never knew what to say to people when they told him that they cared. He was fine telling Emilie or Gram that he loved them, and he was fine giving Uncle John hugs at Christmas, but he never quite knew what to say to those who weren't his immediate family. Not having siblings with him at Hogwarts, Oliver often wondered how it was done in other homes. The Weasley brothers showed camaraderie and amiable good nature among each other, but they didn't traipse about saying 'I love you' and passing out sap.
Katie was like part of his family, just as the Weasleys were, but Oliver wondered if display of emotion was more common in her household, wondered if perhaps she expected him to hug her in thanks or return the sentiment of her compliments to him. Should he treat her as Charlie treated Ginny? Oliver met her gaze, searching her eyes briefly before looking back down at his own hands. He didn't want to hurt her feelings - he did care about her greatly, but he never was able to say such things without blushing. Still, she'd done him such a great favor with Emilie, he supposed the least he could do was thank Katie for caring about him enough to do it and to let her know he would have done the same thing for her.
Oliver reached over and took her hand in his, giving her a smile and her hand a gentle squeeze. He leaned forward then and hugged her to him and kissed her cheek. He was thankful and Katie was important to him and even if she hadn't been looking for a hug or confirmation of their friendship, Oliver felt good to be letting her know nonetheless.
"Ye're one of m'best friends, Katie. I dinnaken wha' I'd do without ye."