Hayeon isn't like actively manipulating him in the end. Like Hayeon genuinely loves the mc in his own twisted way which is why he does the things he does to the mc because he's not okay in the head. But by the end after all they've been through (cus a lot of stuff happens to Hayeon, not enough but he get's his own share of shit to go through largely self inflicted as a way to almost atone for what he's done) but yeah by the end they realise if they try they can be happy together and try lead normal lives. It's ultimately all fucked up because of all the trauma Hayeon put the mc through just because he wasn't taught by his family how to have health relationships. But it technically isn't the worst ending. Because at least he is moving on from the trauma and isn't being abused at the very least.
im crying. please just kill yourself. dead is better than alive at this point