Zeynel’s reasoning for why he refuses to turn Ayse is informed by the concept of predestination in Islam (Qadar). It is a deep, complex philosophical issue/concept (1) (2), and the big thing that grounds Zeynel’s ability to cope with his condition.

Zeynel refuses the choice to cut Ayse’s life short because in his mind, to dictate her death with his own hands, rather than with God’s, goes counter against their beliefs.

But that is admittedly, downstream from the real reason: he loves her and knows she doesn’t deserve to be held down by him, whether by her insistence for him to stay, or, to become djinni like he is. This is a characteristic of him that’s more easily seen in the additional lore material in my *mind*, but his entire relationship with her has always been him choosing selfless sacrifice, by putting her first and valuing her happiness. The only solution in his mind is for them to separate.