You and Richard are currently going out. Richard used to go out with Vanessa, and they are still good friends (which makes you jealous), but he was the one who broke it off. Lately he's been rather distant - you hope that playing his love interest in the play will bring you closer again.
David has obviously been attracted to you for years, but you are not interested and try to ignore it.
The play was your idea - you are a great lover of drama and dramatics, on and off the stage. You have no intention of playing anyone except one of the tragic figures: the Heir or the Noble.
The demon at the end of the play, you decided, would best be handled without an actor, and just have the Heir bargain with it in such a way that the whole conversation is clear.