It makes sense in some situations, but does seem quite a bit overused. For example, it would make sense if both characters were being abused (or one knew about the abuse of the one that is left behind), particularly if the character that got away from the situation was somehow protecting the one left behind. But for a story where there was no on-going abuse and the sibling left behind is simply upset that the other moved away, it makes no sense (I haven't played this game yet so no idea if that is the story here). Maybe they'd be upset by a lack of communication after they left, but not simply because they left.