I remember seeing trailers for/reading about this really surreal movie that was released sometime in the late 2000’s/early 2010’s. All I really remember is there was a woman with short black hair, and I guess she meets this guy and they sleep together?? Except at some point she turns into some black substance or something and it ends with her like walking into the ocean. It was very cloudy/stormy wherever the movie took place and also it had a lot of trees. Please help this is driving me nuts. Pretty sure the movie was in english
This sounds a lot like Under The Skin with Scarlett Johannson: http://www.imdb.com/title/tt1441395/combined
but the ending described by the OP is fundamentally (and elementally) not the ending of Under the Skin.