Cloud and Zack are two sides of the same coin in Final Fantasy VII. What is the history between these two friends?

Cloud and Tifa have arguably always been Final Fantasy 7's main romance, but considering the fact that Remake and Rebirth ...

There's Aerith, the sweet and optimistic new friend who represents hope for the game's dying world, and by extension, Cloud's tortured past. And then there's Tifa, Cloud's childhood bestie ...