Usually the ugly guy in the group tries to talk to a girl, and she takes it as an 'in' to get into the group, where she then finds the one she likes, and they casually talk for a couple weeks. Both wait for the other to show some sign of weakness to seize power in the relationship as the one who is needed most.. and eventually, one will admit they like the other. They start dating.
She gets pregnant, and starts to look less attractive. It makes her insecure as time goes on, and kids start to grow, and his eyes wonder. He works, plays video games too much, and generally loses interest in her as he's already conquered her, and she begins looking for that 'fresh' level of attention she used to get, and starts cheating.
They break up.