The various relationships between Allie and her core group of friends organically evolved into them being a rather polyamorous collective where everybody’s involved with everybody to one degree or another, physically and/or emotionally. It’s outwardly a bit confusing at times, but it works.
Even so, there are preferential intimate connections, like Nicky and Zack here. Nicky’s heavily over-endowed clit occasionally steers her towards (and usually into) Allie, for example, while Zack, for his part, is a muscled-up hornball 24/7 who’s quite open and free with his affections...But the two of them have had eyes for each other ever since being two playfully antagonistic rival neighborhood kids, and still enjoy a mutually competitive relationship of quips, barbs, button-pushing, and rather aggressively enthusiastic coupling 😆