Originally Posted by TheAbominatrix
Explain which? I'll just explain both.
A few people have thought that Cloud has all of Zack's memories and that he gained them through the ordeal in the basement of the Sin Ra mansion, perhaps through an experiment. But Cloud doesnt know everything Zack knows, as proven by the fact that Cloud doesnt recognize Aerith. He may have been told about Aerith by Zack, but of course he wouldnt know her just by looking at her. He may figure that out later, and his attraction to her may even be, in part, because of that. Not neccesarily so, but it could be.
To sum it up: Cloud only knows what Zack told him.
Aerith was Zack's girlfriend. A hint lies in Cloud's first meeting with Aerith, when she talks about her boyfriend who was in SOLDIER (this isnt in the church, but further down the line and still in Midgar). Aerith is reminded of Zack when she sees Cloud. Absolute proof is given if you visit Zack's parents in Gongoga with Aerith in your party.
I like to think that Zack and Aerith are reunited in death and live...er... exist happily ever after,