Aerith still declared Cloud as her boyfriend or lover. A boyfriend or lover cannot be one sided. To call someone your boyfriend or lover the other person has to make it clear that they return the same feelings, right? Right. So even if it is the third person narrative, Aerith still declared a known fact, that Cloud is her friend and her lover/boyfriend/beloved/sweetheart. And a lover/koibito cannot be one sided.
It was some pages back but Ryushikaze actually gave an example or two of when fictional characters have called other characters their "koibito" despite there being no return of romantic feelings on the part of the person being called the lover.
So in other words, no. Aerith calling Cloud her lover certainly shows that she desires/desired him like that but it can't tell us whether Cloud regards her in the same way. (Which at the time he couldn't have anyway because it's been stated he was oblivious to her feelings as much as he was Tifa's).
As to Tifa's statement saying she is like a koibito/sweetheart -even though it is never stated to whom Tifa's a koibito to.- Only that she is like a sweetheart. It never mentioned a name -which would have been very helpful if it did- Unlike Tifa's koibito statement, Aerith's statement is made very clear, there's no doubt in who her koibito is as to Tifa's which leaves it up for debate.
Except Tifa was stated to be a koibito by a creator, out of the game's universe, making Tifa's status as someone's girlfriend as infallible as the word of God. Aerith's words on the other hand were how she
perceived her and Cloud's relationship. (See above for the rest).
Cloud being stated as the person she is a koibito shouldn't be necessary either. Just like it isn't necessary to state she is a mother to
Denzel and Marlene or an ally to
Avalanche and so on. It would be silly to argue she is a mother to anyone but the two children living in her care and in her house, and this applies to "koibito" too. Others have elaborated on this point above.
They put Zack in FFVII as Aerith's first crush because it adds to the love story. I see a lot of Japanese movies/shows/books that always have a past relationship that adds some kind of drama to the story.
True, but that isn't always the case in every single novel with a past love so it isn't automatically the case in FFVII either.
Also, Cloud and Tifa are next to each other on this page! And we all know that means love.
Aren't Tifa and Cloud pretty much always put next to each other/on the same page in official SE materials?
The point is basically that being someone else's "catalyst" shows that the person must be very important to the other. Nothing romantic in itself of course.