I have to disagree with you here. MC has spoken to Zach a few times and given him hints. Zach just doesn't get it. There was the conversation at Heaven's when they were there with Elena and Layla, the scolding when Zach behaved badly towards Elena in the cafeteria, the conversation by the pool, the conversation on the stairs at school, and so on and so forth. Zach, however, is someone who doesn't understand anything at all. His entire behavior is, at best, preschool-level. It was never mentioned in the game, but I'm pretty sure the reason Zach had to change schools at the time was because he was expelled for inappropriate behavior towards girls.