For the answer to the question above, this play of Shakespeare is unfolded on the twelfth Night.
The play starts with Orsino being in love with Viola and then follows Olivia falling in love with Viola who is dressed as a man and in love with Orsino.
The love triangle is solved by the appearance of Sebastian, Viola's twin brother. Olivia marries Sebastian thinking him to be Viola.Thus is Orsino left without a love interest and upon finding out that Viola is a woman he decided to marry her.