Things are different now.
Peter had always believed in Neal's ability to change. Everything he'd done, every risk he'd taken for Neal was based on that belief. He'd come so close to losing everything; throwing away his career and his marriage, the best of himself. All for an illusion.
The truth is bitter. He was played. Used. Seduced.
He fell for the words because they made him feel good and every single one was a lie. Neal can still flash his smile and run his games, but Peter knows he'll never really trust him again.
Kramer was right about everything.