This is based off a book I just read called Underwater by Marisa Reichardt. It is so good, finished it in about a day and a half.

So character 1 has been holed up in their apartment for almost a year after something terrible and scarring happens. They inadvertently play a role in a school shooting by being nice to someone. Now they feel like they can't move past it. They don't go outside anymore, they don't really talk to anyone anymore except their family and psychologist. Then character 2 moves in next door and everything changes.