Nonfanfiction book similar to the last few episodes of supernatural (spoilers to the show in body text)

I just finished watching supernatural and the last few episodes where Cass essentially professed his love for Dean before sacrificing himself has me wrecked. Looking for a non fanfiction, preferably mainstream book, with a similar vibe. Like thriller, mystery, potentially supernatural elements with an unexpected but moving romantic (requited or unrequited) subplot is involved. I haven’t read many if any books like this but the closest I can think of is Under The Whispering Door by TJ Klune if that helps