There is a girl with mother's chlothes on a lighthouse and make love with a man during her little brodher died drown.

It kind of shounds like you're talking about the movie Mermaids (1990) - IMDb (http://www.imdb.com/title/tt0100140/) with Cher and Winona Ryder. In this movie though, it's her little sister that is drowning. She ends up surviving though.

You are an angel.The film I was searching for is Mermaids.

I'm glad I could help.