"Can you make fake marks? You've changed how you look before." Changed his shoe color, if not how they were physically.

Alec has a good idea what a few of those reasons are so he doesn't ask about them. He needs to help Zack calm down a bit and come up with a solution that he can control to the problem. After all, Alec isn't going to be there to watch over him and who knows what might happen. He has no plans on keeping an Eye on Zack for the rest of eternity.