Trying to find the title to a movie shown in US theaters in 1969. The plot involves a brother, his sister, and a female friend. They are in their teens. The sister gets jealous because the brother no longer has time for her. The brother and friend decide to run away... I think. Then I remember rain... a storm... a small boat?. a drowning? This movie was in black and white. It could have come out a year or two before this date. It was a serious drama, ending somberly. Thank you for any input.

I tried British Films website without sucsess, IMDB, and some other search places where you put in some search terms. Anyone know of good sites that specialize in older dramas? Thanks, have a great day.