Sewers. Angel helps Buffy down through a hole in the ceiling. Exposition that they're following a vampire. Buffy mentions that Angel hasn't gotten a tuxedo yet, but he shirtily tells her to keep her mind on the job. The vamp drops down from the ceiling. Buffy: "Not now." She dusts him. Hee. She goes on that every time she brings up the prom, Angel gets grouchy. How can she tell? He struggles with his thoughts (insert "Angel struggling with his thoughts" joke here), and tells her they need to talk, but not now. She tells him to spill it, and that he's scaring her. He says that he's been thinking about their future, and that the more he does, the more he thinks that their being together is unfair to her. Buffy refers again to "Choices," saying that he shouldn't listen to what the Mayor said, because he's the bad guy. Angel says the Mayor was right, and I'm forced to agree. One of the perks of being evil is that you can tell people the truth without worrying about sparing their feelings.
I started to recap the next few lines, but I was basically transcribing them, so -- here:
Angel: You deserve something outside of demons and darkness. You should be with someone who can take you into the light. Someone who can make love to you.
Buffy: I don't care about that.
Angel: You will. And children --
Buffy: Children? Can you say "jumping the gun"? I killed my goldfish!
Angel: Today. But you have no idea how fast it goes, Buffy. Before you know it, you'll want it all. A normal life.
Buffy: I'll never have a normal life.
Angel: Right. You'll always be a Slayer. But that's all the more reason why you should have a real relationship instead of this. This freak show.
Oh, man. That was the point of no return, right there. Buffy backs away in pain. Angel tries to apologize for that remark, and tells her how much he loves her. She says she's thought about these things too, but he can't make these decisions for her. Angel: "I'm trying to do what's right here. I'm trying to think with my head instead of my heart." Buffy: "Heart? You have a heart? It isn't even beating!" They're even on the "ouch" comments now. Angel, wounded: "Don't." Buffy says she can't stop loving him. "I want my life to be with you." Angel, softly: "I don't." She can't believe it, and wonders how she can stay away from him. He drops the bomb that after the Ascension, should they survive, he's leaving town. Buffy finally manages, "Is this really happening?" I think we all know how she feels. They look at each other in tears.