Jackie is Alex and Kayla's older sister...who you slept with, and everyone found out. Kayla believes you seduced her, used and abused and dumped her (despite Jackie actually saying qwuite the opposite). In the last update (or previous..not sure) when you stay at Mei's, Kayla asks you about this and you tell her the full story (which surprise surprise, matches what Jackie told her) and from there, Kayla changes her attitude towards you as she realises you afre nott he asshole she thought you were.
You're saying this entire section of content is missing from the FMC route???