Warning: spoilers ahead for Episode 6! In the first season of 13 Reasons Why, it didn't seem like Hannah and Zach knew each other very well. Though there was the potential for a connection, it seemed like it was ruined after he stole her encouraging notes from the class they shared. That was until Season 2 revealed that they actually dated for an entire summer. They seemed really happy together, so why did Hannah and Zach break up on 13 Reasons Why?
The second season attempted to revisit past events from perspectives besides Hannah's, but no situation was quite as embellished as Hannah's relationship with Zach. Apparently, the summer after the note-taking debacle (when Hannah also shared a letter about her own loneliness with Zach that she thought he threw away), the two reconnected. Many of their classmates were out of town and they kept crossing paths at the movie theater where she worked. Zach became a regular visitor so that he could see Hannah and eventually a relationship blossomed.
Despite the issues they had in the past, Hannah and Zach were able to be open with each other about what they were dealing with. They both struggled with being pigeonholed by their classmates, though that manifested in different ways: Hannah had been saddled with a sexist reputation because she dared to have a crush on a boy, while Zach felt he had to fall in line with his cruel jock friends.
After their talk, they decided to take things to the next level and have sex. Hannah wanted to control her own sexuality after so many people had maligned her and gossiped about her. That had made her feel like sex was a bad thing, so she wanted to be able to have a positive experience on her own terms. They spent the next few months getting closer and the flashbacks made it seem pretty blissful; it was all kissing montages and ice cream cones and sunset walks. So how did it all fall apart?
Part of what allowed Zach and Hannah's relationship to flourish was that they didn't have to deal with all the drama at school. When the summer ended, that started to intrude. Zach told her he didn't want to tell any of his friends about the fact that they were dating because he wanted it to be private, just something between the two of them. Hannah went along with it, but it got to be too much when his baseball player friends mocked her at the movie theater and Zach just stood by, letting it happen without intervening.
Zach apologized, but Hannah chose to put an end to things between them. She told him that if they broke up in that moment, their relationship would "stay good" and not become complicated when real life inevitably intruded. Zach didn't argue even though he genuinely liked her. Not voicing how he really felt was characteristic of Zach; as actor Ross Butler told Entertainment Weekly after the events of Season 1, Zach "didn't have the backbone" to stand up to his friends and express his real feelings about Hannah.
That continued in Season 2. Zach kept everything inside, which prevented him from reaching out to Hannah when they both could have used some understanding to alleviate their loneliness. They didn't have a bad breakup, but they also weren't being totally honest with each other. It was actually a fairly typical situation for a couple of teenagers, especially for a show that isn't always the most realistic, but that didn't prevent Zach from feeling a lot of regret and anger over the choices he made.
If you or someone you know are experiencing suicidal thoughts, call 911, or call the National Suicide Prevention Hotline at 1-800-273-8255.