Other mistake: When Steve wants his money back, Al asks how much was Steve bragging about earlier ($5) he could take and make a fortune, instead of giving Steve $5 it's a $20 bill.
Revealing mistake: Peg is making Al a steak. Problem is the burner isn't even on.
Plot hole: Notice when Steve joins the card game. He looks at his cards and says I'm in. The cards are face up on the table! And for some reason the other players have one card facing out where others can see it.
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