Heartstopper · S3 E4Sleuthed by @shelfsleuth
Heartstopper · S3 E4 · Isaac Henderson · The park
Isaac's tearjerker: The Song of Achilles
Madeline Miller's 2011 retelling of the Iliad as a love story between Achilles and Patroclus won the Orange Prize in 2012, then had a second life on BookTok with videos of people sobbing at the ending. The ending is in Homer. Isaac had about 2,700 years of warning.
Sources: All the books Isaac reads in Heartstopper, season three, Meeghan reads · Every book that Isaac reads in Heartstopper, Kobo · Isaac's reading list in Heartstopper season 3, Nose in a Book · Every Book Isaac Reads in Heartstopper Season 3, Den of Geek · A Complete Heartstopper Book List, The Geeky Waffle