Magic Mountains: WARNING SPOILER ALERT

I don't get it. I thought that he wanted to kill his ex wife, then why was he the one that jumped off the mountain ?

Maybe the director wanted you to think he would "forget her" by killing her. Or maybe he just wanted it to be ambiguous.

His voice-over in the trailer says the two never argued in the mountains and he wanted the chance to leave her (I'm guessing she left him).