All right... *decides to explain self, and is sure there are spoilers abound below*

I know girls like Aeris and I know girls like Tifa.

The girls like Aeris, while they may be open about their feelings and competitive about their men, aren't really all that concerned over sex. Aeris above all wanted Cloud because he made her feel safe and because he reminded her of Zack. I would even go so far as to say that she loved Cloud, and that's a very strong pull in and of itself. Love makes people do stupid things.

The girls like Tifa. The popular girls. The girls all the boy swoon over. They're either nice and innocent, or they're... well, not so innocent. Recall that Tifa had quite a few boys over at her house all the time, when they were, what was it? 14? Come on now, you fellows out there know what life was like when you were 14. Now in my eyes she gave into the "pressure" if you will. That's why she reached out to Cloud that night on the well. He was the only one who hadn't treated her like a piece of meat. She wanted her knight in shining armor to save her. To save her from what? The promiscuous life she was leading. Adding to that are the simple concepts of wearing a short leather skirt into battle and having breasts that cannot possibly be natural, plus several lines she said that were rather... lewd.

Plus I might make one more point; observe how the girls react to the situation at Don Corneos. Aeris treats it like a game, but Tifa seems to have a very serious attitude, knowing about what goes on here, possibly firsthand.

Of course this is just heresay and conjecture and none of you really have to believe my opinion about the sexual habits of fictional characters, but dammit I felt they needed to be shared.