thinking about aeron and davos not worshipping the same gods probably means they won't go to the same heaven (-or hell-) and they know it soooo
them being so afraid that if they die, they won't even reunite in the afterlife and will never see each other again
kid aeron going to his septon and asking where the followers of the old gods go when they die and the septon either telling him they go to the lowest of the seven hells or that they have no afterlife at all and then crying himself to sleep afraid davos is doomed
davos hearing that the brackens felled a weirwood on their lands and praying with all his soul aeron had no part in it, not knowing aeron begged his lord to leave the heart tree untouched
during an argument aeron saying something like "i wish i could die now so i'd be rid of you" and that hitting davos so hard he replies with "well i'd be happy to help you meet your false gods" and then they both regret it instantly
them falling asleep together beneath a weirwood and both getting one of those crazy trippy dreams in which they see themselves dying at each other's hand and being dragged to their respective hells by their deceased family members, and waking up so disturbed they don't talk or see each other for like a month, too afraid they might actually cause the vision to happen
them at the burning mill, realising they could never be together after slaughtering each other's families and both begging the other to kill them out of guilt and despair but neither accepting and fighting to get to die first, arguing that it's their fault, only to die together
probably so many more things that drive them both apart from the sheer terror of making a wrong move that would separate them for eternity and also make them want to enjoy every second they have together because they know it's all they have