He didn't know what else she could do to make him believe, either. She'd done everything she possibly could and he knew that. He loved her for trying as hard as she had been. For holding him through the screaming nightmares. For helping him count his own fingers when he couldn't catch his breath to tell whether or not he was awake or dreaming. But deep down, he felt it. He felt the thing that Deaton had warned them about stirring inside of him, waiting to crawl its way out of him. Waiting to destroy and hurt and do terrible things.
He let out a shuddering breath, relaxing just a little under her touch, the way that he always did. Because she was right. She was his anchor, in more ways than she may have even realized. For several long moments he just wept silently, shoulders shaking until she spoke again.
Stiles nodded wordlessly at her promise, trying to smile but not quite managing it. "We'll just keep researching." He shut his eyes as she kissed him, and he kissed her back, lifting his hands to cup her face and trying to convey everything he felt for her in that one kiss. And hoping to god that it wouldn't be their last.