After helping Phoebe through the darkness

 "After helping Phoebe through the darkness of the Woogyman, Leo quietly left a small letter next to Piper’s pillow. She didn’t notice until the morning sunlight hit the thin white paper.

“Piper,
Sometimes I wish I wasn’t a White Lighter. So I could be with you, like a normal person. But maybe what makes us special is that we choose to love each other, despite our differences.
I’m always here. Even when you can’t see me.”

Piper held the letter, her lips pressed together. The soft sound of wind chimes echoed in her ears from the hallway. She didn’t need to turn around—she knew Leo had just left."