Lie to Me (Season 2, Episode 19):

The kitchen at the Summers house. Buffy is nursing a cup of coffee. Angel slowly pushes the door open.

Angel: Buffy. May I come in?

Buffy: (looks up) Sure. I thought once you were invited you could always just walk in.

Angel: I can. I was just being polite. (closes the door) We need to talk.

Buffy: Do we? (picks up her coffee and heads into the dining room)

Angel: It's about your friend Ford. He's not what he seems.

Buffy: Who is these days?

Angel: Willow ran him down on the computer.

Buffy: Willow?

Angel: We found this address, we checked it out with Xander, and it turned out...

Buffy: (disbelieving) And Xander? Wow. Everybody's in. It's like a great big exciting conspiracy.

Angel: What are you talking about?

Buffy: I'm talking about the people I trust. Who's Drusilla?

Angel lowers his eyes, seeing he's been caught in a lie.

Buffy: And don't lie to me. I'm tired of it.

Angel: Some lies are necessary.

Buffy: For what?

Angel: Sometimes the truth is worse. You live long enough, you find that out.

Buffy: I can take it. I can take the truth.

Angel: Do you love me?

Buffy: What?

Angel: Do you?

She takes a moment to consider her answer.

Buffy: I love you. I don't know if I trust you.

Angel: Maybe you shouldn't do either. (turns away)

Buffy: Maybe I'm the one who should decide!

Angel: I did a lot of unconscionable things when I became a vampire. (turns back, but doesn't make eye contact) Drusilla was the worst. She was... an obsession of mine. She was pure and sweet and chaste...

Buffy: And you made her a vampire.

Angel: First I made her insane. (looks at her) Killed everybody she loved. Visited every mental torture on her I could devise. (Buffy looks away) She eventually fled to a convent, and on the day she took her holy orders, I turned her into a demon.

Buffy: Well. I asked for the truth.

Angel: Ford's part of some society that reveres vampires. Practically worships them. I don't know what he wants from you, but you can't trust him.