Okay, trying to track down 'Dilan Milea' can feel like a bit of a scavenger hunt because it's a multi-part story. I finally found the whole series on Wattpad, which seems to be the primary online hub for it. The author, Pidi Baiq, has it uploaded there. It's not exactly a polished ebook you can buy on Amazon or Kobo, at least not in English. You have to read it directly on the Wattpad app or site. The translation quality can be a little uneven between chapters, but the story's charm still comes through. I'd recommend starting with 'Dilan 1990' and then moving to 'Dilan 1991' and finally 'Milea' to get the full, heartbreaking timeline of their relationship.
A quick heads-up: if you're coming from the Indonesian movie adaptations, be prepared for some differences. The books have a rawer, more internal feel since you're deep in Milea's thoughts. The movies gloss over a lot of the day-to-year time jumps that the Wattpad serialization shows. Reading it this way, you really feel the slow, inevitable drift apart, which makes the ending hit even harder.