Tetsuya Nomura said:
"I don't know if you could really say that FFVII had any unanswered questions to speak of. We just created FFVII with the idea that we wouldn't just come out and tell people the answers. The answers are there, but no one is there to tell you where to look for them. We didn't leave anything hanging."
Now, since this quote proves there are no unanswered questions, I looked into the game to see what the answer to the question of whether or not Tifa loved Aerith is. And I'm going to have to conclude that yes, Tifa did love Aerth. First of all, Tifa says she and Cloud are just friends to Aerith when they first meet. This was clearly so Aerith didn't get the wrong idea about Tifa and Cloud so Tifa could still have a chance with Aerith. Second of all, Tifa is constantly worrying about Aerith after Aerith is kidnapped, and mentions her quite often. Here's the things she says for proof:
Tifa said:
Aerith!!
Aerith!
Oh! Aerith!
You're going to help Aerith?
It's my fault... I was the one who got Aerith involved in this. I feel so depressed.
You're going after Aerith, right? I'm coming with you.
You're right. This is the only way to save Aerith...
Well, we've got to get to Aerith to help her somehow. I don't have time to argue with you. I'm going!
I hope Aerith is all right.
Remember, we're here to save Aerith.
...animal? That's terrible! Aerith is a human being!
Then, when everybody's captured and in the cells, Tifa gets jealous when Aerith mentions a deal to go on a date with Cloud, because she loves them both and if they started dating each other that would suck for her.
Then, when Aerith dies, Tifa touches Aerith's face, then runs off crying, clearly showing Aerith's death has affecting her deeply.
And then, in the ending, Tifa expresses to Cloud her desire to meet Aerith in the Promised Land. Note that Cloud only thinks they could, while Tifa say they should.
And the final nail in the coffin, is the fact that the relationship between Cloud, Tifa, and Aerith is described as a love TRIANGLE. A Triangle has three connected lines in it. We already know there's mutual romantic feelings between Cloud and Tifa, and between Aerith and Cloud, but that only leaves us with two lines, which would give a love v, so there must be a third line between Tifa and Aerith.
And there you have it, Tifa loves Aerith, AerTi proofz ftw.