And precisely because the sex with other guys keep happening offscreen, I haven't even started the quests "Handyman" and "Three's Company" and I won't start them. I shouldn't have started the "teen crush" quest either, but at least you can tell Gabriella that you're not interested in her.
So I hope that if other LIs have the participation of other guys in their paths, it's something completely avoidable (that is, it doesn't happen either on screen or off screen)