The season 2 finale of "Severance" ended with one hell of a moral dilemma: should Innie Mark escape with his outtie's wife Gemma, or should he return to Helly to enjoy whatever remains of his life on the inside? In a pure utilitarian sense, it would be better if he left with Gemma. That way Outtie Mark could get her out of the building safely and explain to her everything that's been going on. This is the best shot these characters have of taking down Lumon; it's also the best chance they've got at keeping Gemma alive, considering she'll be targeted hard by Lumon in the season to come. 

Instead, Innie Mark turns around and chooses Helly, all while Gemma pleads with him from outside the door. It's not clear how much of this situation Gemma even understands, since nobody has told her that Mark is severed. Still, it must sting...