Space Sci-Fi: Long-term Exploratory Mission, Youngish Crew, Told from a single character's perspective (male, no/foggy memory at beginning of story)

[William]

Read: Likely between 1988-1995, no idea how old the book was at the time

I believe it was considered full "adult" sci-fi, but the vaguest memories I do have were that most of the crew appeared to be young adult and can't help but wonder if it might qualify for this genre now.

There are a few distinguishing features, that potentially may be considered spoilers:

1. It turns out the crew is either immortal, or very-very long-lived

2. The main character (male) has his memories reset every X number of years (my memory wants to say 20) to serve as a guidepost to the rest of the crew as to what it means to remain "human" after so many years alive, and on their exploratory mission.

3. One of the most memorable parts of the story, especially given the time period in which I read it, was a male/male sexual experience (I believe it unintentionally became mastabatory), that the protagonist felt some shame about afterwards. Particularly because of who it occured with.

4. One of the rules among the crew was that you had to say "yes" at least once to any romantic interest to reduce hard feelings from rejection.