The Doctor and Companion take in a show, Love's Labour's Lost, and at its end the author announces the sequel, Love's Labour's Won. It's a lost play:: in the first part, four nobles swear off women, shutting down their hearts and devoting themselves to study. Which is to say, they're unwilling to get hurt again; they shut down one of their hearts, so to speak. However, a princess and her retinue appear, for diplomatic arrangements regarding Aquitaine, and the king must make a choice: to let the women in, to let the games continue, even if it means temptation. Even if, in doing his job, he risks breaking his heart again. They fall in love, four brides for four bridegrooms, and just when you think everything's okay, just when you think sometimes happy endings are possible, just when you think endings are possible, the princess's father dies. She becomes a queen. The noblemen are left alone, promising always to love and cherish their ladies, even though they've gone beyond the veil, across the Void. Sound familiar? The nobles are required to wait in silence for a year, without companionship, in order to prove their love. It's a play about plays, a play about words, with more wordplay and word magic than any other thing William's written. Comedies end in marriages, always, and tragedies in death. Love's Labour's Lost is a twisted thing, requiring a sequel, for this reason: all comedy ends in marriage.
I think the way to avoid going nuts with the repetitive romance stuff between Martha and the Doctor -- which is picked up and put down like a rabbit at a birthday party all through the season and which is one of those "arcs" that Torchwood specializes in, telling us something one hundred times without showing us once, and then pointing to it and saying: "Development" -- is to compare this bed scene with "The Runaway Bride" and not Rose's relationship with the Doctor at all. Specifically, the forest/trees metaphor. The Doctor has, in the long stretch of time between "Doomsday" and "Bride," made a conscious decision to turn off his human heart. Donna's pax lies in getting him to verbalize the choice: a very "tree" act for a man who's had to go more "forest" than he's ever had to before. Martha's relationship with the Doctor becomes emblematic of his relationship with humanity, both ours and his own, which is of course mirrored perfectly in the finale: he tries to lie in bed next to us without touching, and ends up nearly dead as a result.