So she's a booty call? D: I never watched Complete
They have an emotional attachment that one has difficulty coming to terms with and the other is somehow patient enough to wait.
Somehow I doubt Cloud is getting out of emo enough to bang her. :p
You have to think back to CC, 7 and then watch AC.
Then you see that Cloud is held back by many things. Aerith being one. Another being the whole Nibelheim incident.
Never got to play CC but they show the Nibelheim stuff in 7 too. I have the "general" idea.
You can watch the CC cut scenes on youtube.
Honestly Crisis Core really explains so much of what is wrong with Cloud.
Like it's told a little in 7, but CC really explains his whole depression based on the illusion of who he thought he was.
Edit: Very messed up, but I find his reasoning justified some what after CC.