I remember this as a YA book in the 70s.
The story is of a girl who goes to live with her Quaker cousins [I think] during the Civil War. There are two brothers. The one brother she falls in love with, Jonathan. The other is her best friend. She's hurt going to the spring house and when Jonathan finds her, she calls out for his brother who died. He thinks she loves his brother but at the end finds out she's calling for him because she thinks she is going to die and she wants him to help her die peacefully. Jonathan then goes off to fight in the Civil War [or before... Not sure of the time line any more.]
It does have a happy ending. I know it was written before 1976 but not sure when. It is typical of the YA but may not be a YA.
Does this book sound familiar to anyone ?
I remember his name as Jonathan but I can't tell you I am right.