The ending of Final Fantasy VII was the most important piece of the game. Although, it seemed more like a cliffhanger. Everyone had their own opinions and speculations on the ending before the sequels and prequels came about. Though, this is mostly opinion, who is to say it is legitimate proof compared to anyone else's opinion?
As of course, every Cloud and Tifa would deny and say that they had hot sex under the Highwind (even though they awake fully clothed) and when Cloud saw Tifa's hand after Aerith's, it without a doubt proved they were meant to be. I honestly don't see how. When Cloud defeats Sephiroth, he is in a Lifestream sort of state, and above he sees Aerith's hand. In which he is trying to get ahold of her, in hopes of being with her. But before he can reach her, the ground below him begins to shake in when he looks up he sees Tifa's hand. That does not necessarily mean his final decision was to be with Tifa. Cloud realizes he is in danger and what do you expect him to do? Not grab on for help? But nonetheless when they reach to safety, Cloud's first words are:
Cloud: "I think I'm beginning to understand..."
Tifa: "What?"
Cloud: "..an answer from the Planet... the Promised Land... I think I can meet her... there."
Tifa: "Yeah.. let's go meet her."
Why wouldn't his initial response be asking Tifa if she was okay, or saying "thanks for saving my ass." But instead, he is thinking about Aerith, while being around Tifa. I can't stress it enough, but that scene pretty much describes how Cloud feels in more ways than one. And I truly believe Tifa realizes this and accepts the fact Cloud does not return the same feelings as she does.