Sir Andrew is aggravated that Olivia favours Cesario and threatens to leave
Aided by Fabian, Sir Toby persuades Sir Andrew that Olivia favours him
Sir Andrew goes to write to Cesario to challenge him to a duel
Maria enters with the news that Malvolio is wearing cross-garters and yellow stockings
Sir Andrew joins the ranks of those in the play who are unlucky, unhappy or unrequited in love, his departure would cut off Sir Toby's money supply and bring his revelry to an end
Sir Toby's greed is his prime motive for his friendship with Sir Andrew, so to keep the friendship, him and Fabian persuade Sir Andrew to write to Cesario about a duel