Graymouse
Pro Adventurer
I believe it's fairly reasonable to say that Tifa felt jealousy in that moment, whether it be because she suspects of a hint of romance between Cloud and Aerith or because she's envious at how easily Aerith got close to Cloud where the latter seems to be comfortable around her. It could be a mix of the both. Of course, it's also reasonable to say Tifa's question to Cloud was propounded due to her genuine curiosity. These feelings can co-exist, you know. They're not mutually exclusive, and Tifa having those feelings simultaneously doesn't make her one-dimensional at all. In fact, I support this reading of the scene because it is consistent with Tifa's insecurities during this part of the story. I say this as someone who stans Tifa: she IS insecure---in her motivations, in her actions with AVALANCHE, in her place in the world, in her memories, and in her relationship with Cloud. It is part of who she is right now and it is her character arc to grow out of those insecurities.
But Tifa feeling insecure does not really confirm anything romantic between Cloud and Aerith, at all (it can only be inferred). It only informs us about Tifa.
I know this has been shared numerous times before (between this thread and in former LTD threads) and I didn't say anything, but I just want to point out now that proto-Rude and proto-Reno designs really amuse me considering how different their final versions became. And of course, there is Tseng the Eternal. He has always looked the same even way back the game's development period.
I get what you are saying but at this point in the game Tifa doesn't really have any reason to be jealous over Aerith, insecurities doesn't always equate to jealousy.