Sam could practically feel the panic radiating from her. Every instinct he had was screaming at him to help her, but was lying to her really going to achieve that? What was the point of trying to maintain something that was already breaking down?
Sam remembered what it had been like when the wall in his head started to come down, it had been gradual and was almost definitely worse than when it had collapsed altogether. Sam's memories were worse obviously, but at least at that point he'd known they were his. The worst part was definitely the uncertainty, not knowing what was real and what was not, and he couldn't watch Lisa struggling through this thinking she was losing her mind when in actuality she was getting it back.
Up to this point he'd been resolutely staring at the floor, now after much wrestling with his conscience he looked up at her. "You're right." He said simply. "It isn't Marrowood." He took a deep breath, there was no going back once he said what he was going to say next. "They are memories and they are real. You just can't remember them properly." He said the words as gently as he could but he was fully prepared that no matter how he said it the effect would be the same.