This was a pretty cool game, I quite enjoyed it, mostly because of it's originality, I can't say I've played anything like this before.
For the people who can't figure out all the endings;
Tragedy Ending; At least one of them falls in the water.
Lost Love Ending; Get all stars in one frame.
I Am Your Moon Ending; Switch the places from the girl and the boy.
Seagull Trip Ending; Put both of them on top of the seagull.
Bring Me The Moon Ending; Put both of them in the boat, wait for the moon to leave and go to the back. Then place the moon in the hands of the boy.