"Why so pale and wan fond lover?" begins with some good old-fashioned teasing. The poem's speaker, fed up with a friend who won't stop moping around about a lady who doesn't love him back, asks:
Why so pale and wan fond lover?
Prithee why so pale?
Asking why his friend looks so "pale and wan" (that is, pasty-faced and sickly), the speaker isn't just asking why his friend seems so ill and gloomy, though he's certainly doing that. He's also subtly mocking his friend for looking like the very picture of a heartbroken 17th-century lover.
To this speaker's mind, pining like that is just plain silly; the word "fond" here doesn't mean "affectionate," but "foolish." If your lady-love didn't like you when you were "looking well," the speaker reasons with his friend, why should she change her mind now that you're "looking ill"? Moping around like this is useless at best and counterproductive at worst.
In this speaker's opinion, then, behaving like a conventional heartbroken lover is both pointless and more than a little ridiculous. He gets that idea across, not only through that mildly insulting "fond," but through his use of rhetorical questions.
Every sentence in these first lines is a question the speaker already knows the answer to. For instance, when he asks, "Will, when looking well can't move her, / Looking ill prevail?" what he means is, "If she didn't like you when you were cheerful and healthy, she certainly won't like you now that you're mopey and sickly."
Phrasing these points as questions, the speaker sounds like he's trying to cajole his friend out of his misery a little: the tone here is both exasperated and affectionate. That becomes even clearer when the speaker repeats the line "Prithee, why so pale?" twice in one stanza. It's as if he's sitting down next to his friend and nudging him: Come on, buddy, why the long face? Hmm?
The meter here also helps to characterize this frustrated-but-caring speaker. The poem uses trochees, metrical feet with a DUM-da rhythm (as in "Prithee"). That stress-first rhythm helps to make the speaker sound forceful and insistent.
The speaker also alternates between lines of:
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tetrameter (four strong stresses in a row, as in "Why so | pale and | wan fond | lover?")
- and trimeter (three stresses in a row, as in "Prithee | why so | pale?")
The back-and-forth pattern makes it sound as if the speaker is in turns cajoling his friend and getting fed up with him—especially when the stanza concludes with two short, brusque trimeter lines in a row!