What immediately came to my mind was the Hooded Swan series.
Here is an extract from a Wikipedia entry on it. I have
bolded a relevant point.
The series is set in the far future and possesses some of the features of
space opera and
planetary romance. It is narrated in the
first person by the main character, Grainger, a well-known independent pilot. He is acerbic, sarcastic, and generally disagreeable on principle, attempting to keep himself isolated from others where possible. He serves as something as an
unreliable narrator with respect to his own feelings and motivations.
To balance this out, Stableford uses the device of an
alien symbiote, referred to as the wind, who is privy to all of Grainger's thoughts and wants to make him a better person. It also calls Grainger out on some of his self-deception.
Grainger is also privy to the wind's memories from times and places unknown to any other human - all of which he keeps to himself, though in several episodes it is clear that the information would have been highly appreciated by Grainger's employers.
