When he returned she didn't know it was him and since he had not accomplished his goal of becoming a First Class SOLDIER, he was too embarrassed to tell anyone except his mother that he returned home.  Then he left and didn't meet up with Tifa until she found him in Midgar at the train station years later.  In every scene with anyone up until he met Aeris he was pretty cold to everyone, especially Tifa.  Notice how in the game, he was very cold to everyone in the beginning.  He didn't smile or laugh or joke around.  When he met Aeris, however, he let more of himself out and seemed to be more comfortable and considerate.  She made him laugh and he learned to care about something other than himself.  When she died, he was devastated and actually cried, something he had never done in the game up to or after that point.  He was visibly upset and actually showed some emotions, something that it seemed Aeris had awoken within him.  A common argument is that Aeris only liked the "Zack" in Cloud.  I don't believe that is true, because she openly admits that although he reminded her of Zack and that is what initially attracted him to her, she knew he was different and wanted to get to know the "real" Cloud.

        Cloud and Aeris are two of my favorite video game characters.  I love their story and enjoy watching it play out even years after the initial game through Kingdom Hearts, Advent Children, and whatever else they decide to come out with.  The whole debate over who Cloud loves really doesn't matter to me anymore, because there is really no point in arguing it.  Just let everyone like the pairing that they want and then everyone is happy.