As almost everyone knows by now, Aerith ends up getting killed by Sephiroth ... the original and makes it unclear whether she's truly dead or has a chance of coming back due to the multiverse ...
But this is not the world we know. For Cloud to be in the state he is and for Aerith to act the way she does, Zack must be dead. This is one of the clearest indicators of the multiverse ...
Quite a contrast to Cloud Strife's stoic personality, Aerith's bubbly persona has enamored many fans both through the original PlayStation game and more recently, through the modern remaster.