Jack loved high places; you could see forever if you were high enough. He had no fear of falling from them because really, what was the worst that could happen? He’d smash himself up, die and come back healed. Or mostly healed anyway. Sometimes he came back before everything was completely fixed, which could be unpleasant, but not to the extent that he feared it.
Besides, if the building was tall enough, falling was actually quite enjoyable, at least until he reached the ground. No, falling from a building was fine.
It was falling in love that he really feared.