I ran into the same wall trying to track down 'Bad Buddy' as a proper novel translation. From what I've pieced together, it originated as a Thai BL series, not a traditional novel first. There's source material called a novelization that came after the show, but a complete, official English translation just doesn't seem to exist online in one place.
You'll find a ton of fan translations of snippets, episode novelizations, and extra scenes scattered across platforms like Wattpad, Tumblr, and Archive of Our Own. The quality is a total mixed bag, though. Some translators are meticulous, others are basically summarizing. If you're desperate for the story in text form, those fan works are your only real option, but don't expect a polished, cohesive book.
It's a bummer because I'd love to read a faithful adaptation of Pran and Pat's dynamic. For now, I just rewatch the series and hunt down those translated bonus chapters for extra crumbs.