I read a short story 1-2 years ago and I don't know the title/author. The story was online, possibly at Longform, although it does not appear to be there. I don't recall if the story itself was new or old.
The protagonist, a boy (maybe his name was Harry/Henry?) develops a friendship with a a girl (Emily? Ellen?) at an orphanage/boarding school.
They are not raised by parents, but by caretakers, and the children are separated from society. When the children are scheduled to leave, they never return or keep in touch with old friends.
When Emily is scheduled to leave, Henry make plans to meet her again, after he leaves. Somehow, Henry realizes that the none of the children graduate or leave; instead, they are killed by a planned revenge murder.
His caretaker explains that another man hated his wife, who left him. Emily was raised (bred? born?) so that the man could satisfy his murderous desire by drowning Emily, who looked just like his ex-wife. Meanwhile, Henry realizes the same fate awaits him. He was raised to look exactly like Hitler, including the haircut and mustache. An old man, who lost his family in the Holocaust, wanted to satisfy his rage by killing Henry.
These are all the details I can recall.