Best Friends, and The Yellow Crayon speech.

I couldn't find a video of this scene. But it's still precious. 

Willow: You can't stop this.

Xander: Yeah. I get that. It's just, where else am I gonna go? You've been my best friend my whole life. World gonna end, where else would I wanna be?

Willow: Is this the master plan? You're gonna stop me by telling me you love me?

Xander: Well, I was gonna walk you off a cliff and hand you an anvil, but it seemed kinda cartoony.

Willow: Still making jokes.

Xander: Well, I'm not joking. I know you're in pain. I can't imagine the pain you're in. And I know you're about to do something apocalyptically evil and stupid. And, hey, I still wanna hang! You're Willow.

Willow: Don't call me that!

Xander: The first day of kindergarten, you cried because you broke the yellow crayon and you were too afraid to tell anyone. You've come pretty far. Ending the world - not a terrific notion... But the thing is... yeah, I love you. I love crayon-breaky Willow and I love scary, veiny Willow. So if I'm goin' out, it's here. If you wanna kill the world, well, then start with me. I've earned that.

Willow: You think I won't?

Xander: It doesn't matter. I'll still love you.