But he winks, and you drop the subject

You take David's wink to mean that he remembers exactly as much as you do: you're the real David in a Jessica suit, he's the real Jessica in a David suit, Trish is presumably still a clone of Jessica in the Trish suit made from Trish -- and that you're all staying as you are indefinitely, perhaps for life, and behaving as if those magical pen-shaped things never existed. You go along with it.

Months pass and your previous life as David fades like a half-forgotten dream. You simply are Jessica and you love being you, love your family, love your boyfriend David. Makeup and girl clothes and menstruation are just normal. You never think about your former life. But one day you start to notice a subtle change in someone in your family and you remember the pens.