It’s a novel I read as a teenager, so in the early to mid 2000s, but it was an old copy of a book, so I think it was published in the 80s or 90s. It was a very thick paperback, dark cover. I remember very little about it even though I read it several times. The main character is a man and he ends up on an island, stranded it seems. Very few other characters, one male professor-type and a woman with whom he has sex in the ocean (it was not a YA novel, lol). It’s none of the obvious man-stuck-on-tropical-island books, but the ubiquity of that trope and my terrible memory have made it difficult to find. If this strikes a note in anyone’s memory, I’d really like to revisit this book and find out why I read it so much!
Lost Classics of Teen Lit: Name That Book! 