Couldn't Diana act romantically?
Diana: Do you have your own room?Then they go and have sex (the movie skips to the "after" point). Diana made it sound so... technical. After all, they liked each other. Diana wanted to have sex with Alex, fine, couldn't she make it sound a bit more *romantic*?
Alex: Yes. Why?
Diana: Well, call me old-fashioned, but I'll be damned if I'm having a child with a man I've never even slept with.