i mean i liked gizel before so im just gonna say that this whole situation is 50%-50% each other fault:
> she's wayyyy too dependent and possesive of him, kinda understandable since he was the only person close to her and she was already taught that she would marry him, so she ''knew'' they were gonna be together forever.
> he chose the worst fucking method to escape his situation, he had time to try to find a less disruptive way but his interest in seeing the world took priority over his rationality, and we can see here that after discovering the tampering of his golem he realized that the mental stability of his sister is gone, but thks to his self exile he cant even go back to try to explain things anymore, if he gets back he can never leave and if he doesnt come back the sister will keep getting worst and worst
its a fuckfest of a situation even without the dark shadow about to possess the broken sister