I've always felt that Cloud's reaction to Aerith's death and the guilt he felt had something to do with the Zack in him as well. I mean the real Cloud obviously felt guily too, since Aerith was a very dear friend to him, but I think a part of him was playing off Zack's emotions as well. That's just my personal interpretation of it.Zack would feel regretful if he ever lost Aerith during Crisis Core, wouldn't he? He even goes far as toI think it's something to do with Zack in general, but I could be wrong.protecting her from the robot that comes into the church (the scene where the Angeal copy protects them both.)
Here's a cute cloti fanfic I found. Some of you may have already read it, but I still think it's worth sharing.
http://www.fanfiction.net/s/3798564/1/Full_Circle