The Diary of a Strange Man

In a galaxy close to the Solar System, there is also a planet inhabited by humans. Some people among the humans in that galaxy wonder whether humanity originated on Earth or on their own planet, so they send people to Earth to investigate in secret. A young man comes to Earth because of his first love, so he also signs up to come here and find her. Who would have guessed that ten years would pass without him finding her? He decides to try to contact her by publishing his diary.