I have never chained your limbs, Astair, free as the winds that whirl, Go if you wish.
Have you ever set someone free, even though you loved them very much? Have you ever set someone free, because you loved them so much?
If so, you know how the King of Midian feels.
In this line, the king is reminding Astair that he has never kept her against her will. (I guess the time she spent as a slave doesn't count). And if she really wants to go, she can. She can go and be as "free as the winds that whirl", which means that she can be as free as a whirlwind.
On a side note, notice the abrupt rhythm change. I think Howard does this to increase the drama of those words: "Go if you wish."
since less to you is an empire's pride
Than the open lands where the tribesmen ride,
Paraphrased, it might sound something like this:
If you stay here, I'll make you the pride of my empire. (I'll make you the thing that my empire is most proud of). But you don't seem to care about that very much. It seems to me that you would rather return to your homeland, to the open lands of the desert, where your tribesmen ride horses and camels. If that's the case, you can go.
wooing the desert girl.
Ouch, this line hurts.
Apparently, those tribesmen riding their horses and camels through the desert—they're wooing her. (To woo someone means to chase after them, trying to get them to marry you).
And that, I guess, is one more thing that Astair misses about her homeland: She misses having all those handsome, young, hawk-eyed men chasing after her. Astair, it seems, is a bit of a flirt.
It's what they call "adding insult to injury". It's bad enough that she wants to return to her homeland. But to think that she may eventually find happiness in the arms of . . . who? A common goatherd? Ouch!
The poem ends there. And I like how it ends with that phrase: "desert girl." It's the first time the king tells us who Astair really is. She's not a slave—not anymore, at least. And she's not a natural-born queen. Nor is she defined by her nationality or her religion.
She's just a simple desert girl—a girl who grew up in the desert. And keeping her cooped up in the palace would be as cruel as keeping a bird inside a gilded cage.