I think the devs were really trying to thread the needle with Aerith's character, but the problems are: 1) They're not very good at writing women. 2) They greatly underestimated how insanely misogynistic this fandom is.
I think we are meant to assume that Tifa and Aerith have talked about their "first loves" and picked up their conversation after the Shinra Cruiser, because in Gongaga, Tifa is clearly already aware of Aerith's relationship with Zack. I don't see a world where Aerith would tell Tifa about Zack, and Tifa wouldn't tell her about Cloud. (Yuffie clearly also knows about Tifa's childhood crush, though it seems Tifa is more tight-lipped about her current feelings for him.)
The thing is, I think Aerith is obviously aware of Tifa's feelings for Cloud, but I also think her actions show that she is taking Tifa's feelings into consideration? Aerith wants to see if she can fall in love with Cloud to prove to herself that she can move on from Zack, but I don't think she wants/needs him to reciprocate. Even the "dream date" at the end, it's all about Aerith trying to figure out her feelings for him. She never asks him about his feelings for her, because that's not what the "date" was about!
Even without her memories of the future, I think Aerith knows that Cloud and Tifa belong together, and she's trying to help in her own way. Why else would she make Tifa the topic of conversation at Kalm and Nibelheim? Cloud wasn't the one bringing her up!
Therein lies the tragedy of her character. Her friendship with Tifa is one of the (many) things that prevents her from earnestly pursuing Cloud and being able to actually move on. (Which isn't even taking into account the fact that the whole point is she can't move on from Zack, Cloud would never be able to reciprocate anyways because he's not himself/obsessed with Tifa, etc., etc. CA is doomed from so many different angles, but that's also what makes it such a great vehicle to explore all these different relationship dynamics.)
If you legitimately think it was the devs' intent to portray one of the games heroines as a backstabbing hussy, like please step away from the keyboard and go read a book or something, lol. (To be clear, I don't think that's anyone here!) Like with AC(C), I think it's hard to discuss Rebirth!Aerith because the execution of her arc was so far off from their intent, so we just end up talking over each other.