Imaginary girlfriend

I have tried to search for the title of this movie by details for the longest time. I watched it about 5 or 6 years ago and can't remember the name. I know there is this man. He meets this girl who seems to good to be true. She always randomly appears at just the right times. I know the girl is blonde and the guy is brunette. I remember one scene they are kissing in a pool after hours and kiss under the water and there is a beautiful scene where jellyfish are surrounding them ( this man is imagining it all). There is another scene where he is walking through the woods and the animals look like cartoons. At the end of the movie the man looks at the photos he took with her and realizes she never existed.