I also agree that the ending should be improved. I can accept an open ending where you end up looking for a way for him to see the sun again (or to cure him from vampirism). But the way he burns and becomes a joke doesn't work in a situation where the relationship (romance or friendship) is good. Maybe they should have offered a choice in a dialog. So, yeah, you can be a jerk and joke about him not seeing the sun again. Or you can cover him, help him in any way or go with him. Choosing for the player and doing it in a way that most dislike is wrong. It would be like forcing all players to become Illithid no matter what in a way that is passed as the character's choice. It is taking away agency in a wrong way.