[watch the scene]
Peyton: I was reminded today in a roundabout way that the most perfect act of love is sacrifice. That's what Keith did for Karen. Burying his feelings for her all those years so he could be a good friend.
[takes Lucas' hand]
Peyton: I love you, Lucas and I think I have since the first moment we locked eyes. And it is gonna suck but if what you want is for me to let go then I'm gonna do it. Be happy, Luke. I want that with all my heart.
[kisses his hand then walks away]
This scene always breaks my heart. It really shows how much Peyton loves him. I think it shows just how brave and selfless she is. This is why it's one of my favorite Peyton scenes and why I used it.