All I remember is the movie is from the 80’s or 90’s

At the beginning the brother and sister are young and he gets a rabbit, somehow the sister accidentally causes it to die.

At the end of the movie (when they’re grown up) there is a flood and the sister meets him at the tree house. He falls in the water and gets tangled up in the ladder rope and drowns. She tries to save him and once she realizes he was dead, stays in the water and takes her own life.

It’s been racking my mind for years!