All the girls give senpai their attention and he gives his attention to them too, except one girl and that girl is you. You don't care what it take or what will happen but one thing is for sure, senpai will be yours only.
The three will not love the reader as if a crush or anything.
They might just be protective, or think of him as a child of their own.
Maybe they might act a bit yandere, (they'll act possessive over (Y/N), and will end up killing for him to stay by their side. Don't worry, they'll kill for (Y/N) just because they want him by their side at all times, and think of him as only THEIR child.)