There is no unrealistic behavior on this show where society starts to break down when all the adults die in this small town. Between portrays girls the way they really are, with no sugar-coating. There are a lot of examples but I want to focus on one.
In S01E03 "Crossing Lines" written by Malcolm Macrury, it is two weeks after the town has been quarantined. Ronnie, the drug dealer, has been accused of something but he is innocent because he was banging Stacy that night. He needs Stacy to clear his name so he goes to ask Stacy for help...at her boyfriend's house.
Stacy is not happy: This is Chuck's house, you idiot. If he walks through that door I'm yelling "rape"
This cheating girl tells her side-man what she will do to keep her beta bucks BF (he's rich) but this idiot doesn't listen. So while Stacy's beta Boyfriend Chuck is out all night trying to maintain order in town, Ronnie ignores her warning & bangs Stacy again that night.
The next morning Stacy tells him that she won't clear his name because what I have with Chuck is good. Actually it's great & I'm not going to throw it away for you. Ronnie doesn't know that Hypergamy doesn't care.
This idiot ignores her 2nd warning & begs her to help him, so Stacy assures him that she will clear his name & explain it to her boyfriend. He asks how & she replies You're just going to have to trust me.
When Stacy sees her boyfriend nearby, Stacy punches Ronnie in the face & lies to her boyfriend that Ronnie attacked her.
Later that episode cuckold Chuck get his hands on Ronnie's phone & finds out he's been cuckolded & dumps Stacy.
This is what girls do because they don't think about the consequences. Learn how to protect yourself so you don't end up like either Ronnie or Chuck.