Forget Romeo and Juliet, the most romantic play by Shakespeare I've ever read is Twelfth Night. And I'm going to quote an example to prove my point.
Some background info for those who aren't familiar with the play: Viola is dressed up as a boy named Cesario, and is Duke Orsino's servant. He has no idea that she is a girl. Duke Orsino is now sending "Cesario" to Lady Olivia to court her for him, even though she's already told him a thousand times that she's not interested.
Cue this conversation:
VIOLA
But if she cannot love you, sir?
DUKE
I cannot be so answer'd.
VIOLA
Sooth, but you must.
Say that some lady -- as perhaps, there is --
Hath for your love as great a pang of heart
As you have for Olivia: you cannot love her;
You tell her so; must she not, then, be answer'd?
DUKE
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 call'd 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.
VIOLA
Ay, but I know, --
DUKE
What dost thou know?
VIOLA
Too well what love women to men may owe:
In faith, they are as true of heart as we.
My father had a daughter lov'd a man,
As it might be, perhaps, were I a woman,
I should your lordship.
DUKE
And what's her history?
VIOLA
A blank, my lord. She never told her love,
But let concealment, like a worm i'th'bud,
Feed on her damask cheek: she pin'd in thought;
And, with a green and yellow melancholy,
She sat like Patience on a monument,
Smiling at grief. Was not this love indeed?
We men 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.
DUKE
But died thy sister of her love, my boy?
VIOLA
I am all the daughters of my father's house,
And all the brothers too; -- and yet I know not.