The conversation between Orsino and Viola/Cesario in Act 2, Scene 4 is rich with foreshadowing and irony. Having deduced that Cesario is in love, Orsino argues that, since women's beauty fades with age, Cesario should marry a woman who is younger than him. Otherwise, his affection will fade just as quickly, since men are less faithful when it comes to love than women are.
Orsino: For, boy, however we do praise ourselves,
Our fancies are more giddy and unfirm,
More longing, wavering, sooner lost and worn,
Than women’s are.
This statement foreshadows the end of the play, when Orsino forgets his supposed love for Olivia the instant he discovers Viola's true identity. In keeping with his argument, Viola, the woman he eventually decides to marry, is much younger than him.
Later in the same scene, Orsino argues that women do not love as ardently as men do:
Orsino: There is no woman’s sides
Can bide the beating of so strong a passion
As love doth give my heart; no woman’s heart
So big, to hold so much; they lack retention.
Alas, their love may be called appetite,
No motion of the liver but the palate,
That suffer surfeit, cloyment, and revolt;
But mine is all as hungry as the sea,
And can digest as much. Make no compare
Between that love a woman can bear me
And that I owe Olivia.
This argument is hilarious in its hypocrisy, since moments earlier Orsino stated that men fall out of love more easily than women. His claim that no woman could love him as fiercely as he loves Olivia is also ironic because, while Orsino's love for Olivia is entirely performative, the love that Viola feels for Orsino is entirely genuine.
In response, Viola asserts that, while men may be very effusive when it comes to expressing their love, this performance does not reflect sincere feeling:
Viola: We men may say more, swear more, but indeed
Our shows are more than will; for still we prove
Much in our vows but little in our love.
Orsino dismisses this argument, but it is evidently true—while Orsino conceals his lack of true emotion with grand romantic gestures and flowery poetry, Viola remains silent despite her ardent love.
