The Duke is in love with Olivia, at first, who is in love with Cesario. The problem is that Cesario is actually Viola, disguised as a man. Viola is in love with the Duke and working for him as Cesario while being the messenger for the Duke when he wants to send messages to Olivia. The Duke is completly oblivious of the true nature of the whole situation. He believes that Olivia is mourning when she in fact loves Cesario.
I say C. Blind to the truth because I read a shorter version of that book before, and I remember that the duke thinks that Olivia actually like him but hides it. And how he gets mad when Olivia falls in love with Viola, thinking that she was a gentleman! Ha! ;D Hope this helps and have a great day!
