I have reached Rank 7 with Fuuka, and she will become upset if i go out with another girl. So, if i just Establish the Lovers social link with Yukari, without interacting any further with that social link, will Fuuka still become upset and go Reverse? And will Yukari go Reverse if i continue to hang out with Fuuka or do you have to reach the "She might become upset if you go out with another girl" with Yukari for that to happen?
It's also a 60-day time limit for girlfriends (not 90 days).
90 days is the time limit for certain other non-girlfriend school links (Magician, Chariot, Temperance, Fortune)... i.e., any school link that can call you at night, OTHER than the five girlfriend links.