Frat Chance - S7-E6
Continuity mistake: When Bud is talking about this being the year he will get a real girl, he drinks from the carton of milk and spills some on his shirt. Next time they show him the spot on his shirt is dry. The next it's wet again, and it goes back and forth for the entire scene.
Answer: It's implied that Steve filed for divorce since in s04e16, "You Gotta Know When to Hold 'Em", Marcy says that Steve is suing for alimony. Alimony is something that has to be requested when filing for divorce. Although the show doesn't spend time on the actual legal proceedings of their divorce.
Bishop73