Complex sentence: At a party Alison and Sidney's relationship grows when she reveils she's just ended an affair with Lawrence, and he stops her from driving home drunk, missing his opportuinity to sleep with Sophie.
Split into simpler sentences: At a party, Alison and Sidney's relationship grows when she reveals she's just ended an affair with Lawrence. Sidney stops her from driving home drunk, causing him to miss his opportuinity to sleep with Sophie.