My theory is that it all started with Taehyung accidentally killing that guy back in I Need You He regrets his actions and that's what you see he's haunted by it and feels he deserves the same fate so that's why he jumps at the end. All of the footage of the other members is actually what follows Taehyung's jumping (his death). They lost their friend and feel they've all lost a part of them so it's what leads to their actions. In the prologue Jin is recording but think that's just his memories and its what happens after his story in I Need U. Jin is in a sanitarium (the room he is in), following his friends' passings. The gas station part in the prolouge, is actually Jin travelling alone. A stranger takes his photo for him. That's why you dont see Yoongi in the photo. Hes trying to relive his memories with his friends by going places and doing things they used to do. The credits is him stopping by where it all started (with Taehyung jumping)