What similarity is there between what is happening with Tyler and Diane in the present and what is happening between Jason and Tyler in the past?

Tyler and Diane are fleeing from the motel in Padang, Diane finding them a way to safely emigrate (although we do not yet know where they will emigrate). Thus, Diane at this point is taking care of a weak and sick Tyler. In the past scene in this chapter, Tyler goes to take on the responsibilities as Jason's physician, and it is hinted that Jason may be ill and Tyler will care for him. Thus, Tyler is involved with both twins in mirror circumstances--in one, an ill Tyler is being taken care of by Diane; in the other Tyler is caring for Jason who is ill.