Are you talking about when Cloud goes on the date and they go to the Event Square and they perform the play with the other actors?

Two go together, though one resists, (Cloud doesn't want to go onstage)
Both as ones who don't exist. (They are both acting)
He determines what's in store, (Cloud makes several choices through the play)
She's the one from three before. (The date's character is Rosa, lead female from FFIV, three FFs prior to FFVII)
Choosing her is the "correct" path, (You should save your date)
But choose her foe and you'll face her wrath. (If not, she'll slap/punch you)