After Bryce blows out Zach's knee at the Homecoming football game, angry that Zach has "stolen" Chloe from him, Zach goes to the hospital, but he doesn't stay there. Zach later confesses to Deputy Standall that he followed Bryce to the pier and beat him up, stomping on his knees and throwing Bryce's phone into the water. Though he did hurt him, Zach makes it known that when he left the pier, Bryce was still alive. When Zach learns that Bryce died from drowning, it's made clear that Zach believed himself to be Bryce's killer this whole time, though he isn't the one responsible.
At Bryce's funeral, Zach and Chloe are seen sitting next to each other, which seems that these two might develop a romantic relationship in season four.