Two to five people can play Marriage Material with one deck.
If you have more than 5 players, it is recommended that 2 decks be combined. If you play with 2 decks, it is suggested that a "no duplicates" rule is instituted; a player cannot play two or more of the same Excuse on a Commitment since your Significant Other will not accept the same excuse twice at the same time.
If the Commitment happens to make its way around the table and back to you, then you may play the Excuse again but still only a single time. After all, you could still have the same issue that you did the first time you got out of the Commitment.