it was...from the beginning it was obvious that Peter had feelings for Gamora, but it wasn't clear whether she had the same feelings for him, and that scene basically confirmed that she does indeed love Peter the same way he loves her
Even though it wasn't an obvious direct confirmation until Infinity War, and those who haven't watched the GOTG movies or haven't paid close attention probably would've missed the message of that significant Starmora scene, but for those who have watched the GOTG movies and have been paying attention, we all knew that scene was the first confirmation of Starmora's love for each other