Strictly romantic option: Jonathan finds a way to visit Arabella for a few hours one night for a sweet and steamy reunion. Perhaps he is affected by the magic that possesses him in some way: maybe it makes him not completely solid or causes him to fade in and out between being completely physically present and just an illusion. Or perhaps the magic that surrounds him makes the experience all the more pleasant for both him and Arabella.

Bonus crack option: In order to be able to come to Arabella, Jonathan requires not only his own power but Norrell's as well. Meaning that Norrell must remain in the room during Jonathan and Arabella's "activities." Norrell either hides in a corner with his face to the wall and his hands covering his ears, or - if you prefer - he totally enjoys the show.