Earthbound.

At eleven years old Joe Norman is told by his dying father that he is an alien hiding on earth. Joe believes him. He grows up to be a die-hard fan-boy working in a comic shop. When he falls for down-to-earth Maria, a fellow sci-fi fan, he is inspired to lead a more normal social existence. Until intergalactic bounty hunters track Joe down at his new office and the couple soon learn the dangerous truth about who Joe really is.