A book that you wish more people would've read.
"The Boy I Love" by Marion Husband (the whole trilogy)
In fact, every book she wrote, so also
"Say You Love Me"
"The Good Father"
"Six Little Deaths"
It frustrates me no end, that such a superb writer, someone who makes me writhe with envy, is overlooked by the "serious readers" because she writes about taboo topics including LGBT ones, and by the m/m crowd, because she takes things seriously (and isn't writing fluff). She writes on Booker or Orange Prize level, and any of her full novels could have run rings around e.g. "The Song of Achilles" which reads like Mary Sueish fanfic instead in direct comparison.