As to the game, by the way, Sephiroth never considered Cloud a friend. Until Cloud hurled him into the reactor, he probably didn't even notice him. Cloud, remember, was not a member of SOLDIER; the "Cloud" that interacted with Seph in the Kalm flashback was, effectively, Zack. I can understand that you disliked the original game, now, given that you missed the single most important plot point in the story.
Really, given what transpired, Sephiroth should have nothing but hate and resentment for Cloud.
Also, ignoring that you miss both the plot and symbolism in both the original game and Advent Children, Kazushige Nojima, not Tetsuya Nomura, was primarily responsible for the story of Advent Children. And, given that his story was based on what actually happened in FFVII, I'm inclined to prefer it to your take.