The meter of "Porphyria's Lover" is fairly regular iambic tetrameter. Wait: before you zone out, let us explain. The meter refers to the pattern of stressed and unstressed syllables in the line. An iamb is an unstressed, followed by a stressed syllable: da-DUM. So "iambic tetrameter" describes any poem with four (tetra=four) iambs per line: da-DUM da-DUM da-DUM da-DUM. Check it out:
The rain set ear-ly in to-night,
The sul-len wind was soon a-wake,
It tore the elm-tops down for spite,
And did bits worst to vex the lake:
Try reading those first four lines out loud – the stressed syllables fall on where we've made the text bold and italicized. See how even the rhythm is? But then it all goes out the window in the next line:
I list-ened with heart fit to break.
Whoa! The line starts out iambic, but then you have two unstressed syllables in a row, followed by two stressed ones in a row. What's up with that? Did Browning just mess up? Hardly: Browning establishes that regular iambic tetrameter in the first four lines in order to create the anticipation for a regular meter throughout. When that meter fails, it's always for a reason. In this line, the speaker refers to himself for the first time, and it's to say that his heart was breaking. So the regularity of the meter breaks, just like the speaker's heart! Oh, Browning, you sly dog. Keep an eye out for other spots in the poem where the meter breaks down, and see if you can figure out why Browning does it (hint: he's too clever a poet to do anything by accident!).
That covers the meter, so what about the rhyme? You've probably already noticed the rhyme scheme – it's pretty regular, and follows this pattern: ABABB, CDCDD, EFEFF, etc. The rhyme is regular, but it's asymmetrical. Each rhyming unit is backloaded: there are more "B" rhymes than "A," and more "D" than "C," etc. What's up with that? Well, some critics like to argue that the unbalanced rhyme scheme reflects the speaker's unbalanced mind. You might have a different impression – how does the asymmetry of the rhyme scheme impact your reading of the poem?