I support C/T for several reasons.

*Aeris never knew the real Cloud...the Cloud before the events at Nibelhelm. Tifa did.

*Studies have shown that people who have known each other from childhood are more likely to get together in a lasting relationships than does that haven't. This study was not limited to just childhood friends BTW.

*I think Cloud looked to Aeris as someone to protect, to act as a Guardian to. That's just my three cents, however.