My plot suggestion: After Joseph leaves, he returns to Anna's doorstep at some point and asks her to forgive him. Anna refuses and tells Joseph she no longer needs him (the dialogue will be different between the Pure and Slut routes, but the meaning is the same). Finally, the protagonist and Anna have sex in the doorway while Joseph watches.The protagonist and Anna can say something to provoke Joseph to make him feel sad, or make Joseph realize that this is a conspiracy planned by the protagonist (since the player actively chooses to let Joseph leave and occupy Anna, don't think it's too much to do so)