When Love with unconfinèd wings Hovers within my gates, And my divine Althea brings To whisper at my grates;
The poem opens with the speaker telling us what happens when Love comes to town. Specifically, Love shows up with a pair of "unconfinèd wings."
"Unconfinèd" means not confined or imprisoned. So, in other words, the speaker uses a metaphor to compare Love to some kind of bird that is free to fly wherever it wants.
Where has it gone this time? Well, it's inside the speaker's "gates." Now, it could be that the speaker is talking about a fancy house with gates on it, but we have history on our side to tell us otherwise. In this line, "gates" likely refers to the gates (i.e., the entrance) of a prison. In fact, it might also be a clever allusion to the prison in which Lovelace was confined in 1642: Gatehouse Prison.
And hey, Love brought a guest—"divine Althea" has come to visit our speaker in prison.
"Althea" is a woman's name, but this is most likely a reference to a real woman named Lucy Sacheverell, who some say was Lovelace's fiancée (not much is known about her). "Althea" is also an English version of the Greek name Althaea, which means "healer." This suggests that speaker thinks of his lover as a healer and source of comfort.
Although "brings" is at the end of line 3, the bringing is being done by "Love." In other words, normally we would say "when Love brings my divine Althea," but here the syntax has been rearranged to keep the rhyme scheme intact. (For more on good stuff like rhyme, check out "Form and Meter.")
Althea is whispering at the speaker's "grates," which refer not to his barbeque grill, but to the bars of the speaker's prison cell.
This all sounds very magical. Love metaphorically flies to the speaker's cell (in contrast to the speaker, who is "confined" in prison), and brings his girlfriend to him so she can… whisper.
Notice that we don't know what happens "When" Love actually shows up with Althea. So far, we only have the set-up of a long sentence. When Althea shows up, what next? Maybe things will make more sense as we keep reading.
When I lie tangled in her hair And fetter'd to her eye
Nope. Here the speaker just adds to his "When" clause (i.e., the first part of the sentence that takes the form "When x… then y"). So, we can assume that "When [he] lie[s] tangled in her hair / And fetter'd to her eye," eventually something happens.
("Her" here probably refers to Althea, though it is possible that it could refer to "Love" as well. Still, we think it makes most sense to see these lines as describing the object of his love—Althea—rather than Love itself.)
To be "tangled," is to be wrapped up, but this kind of constraint (in a person's hair, as in an embrace) seems much more pleasant than, you know, chained up in jail.
As well, "fettered" also means chained or shackled. It's a bit of a stretch, but here the speaker is claiming to be metaphorically shackled by Althea's eyes.
Just pretend Althea's eyes are like one of those cannonballs attached to a chain that prisoners used to wear around their ankles. Actually, that's kind of gross (who wants to be chained to an eyeball?). The better way to think of it is that the gaze of Althea is so intense that the speaker seems to be paralyzed by it.
Yup, love can do that to you alright. But the use of "tangled" and "fettered" here show us that prison is always on the speaker's mind, and he thinks of everything in terms of confinement.
Or maybe he's just trying to imagine prison or confinement in a different, and better, way.
It's important to remember, also, that this Althea person, the speaker's love, is not really there in the cell with him (unless you think Love can actually sprout wings and act as a personal jetpack). Instead, the speaker simply imagines that she is there.
Love has the power to make absent people (Althea) seem like they're present. Sweet!
The birds that wanton in the air Know no such liberty.
Aha! We finally learn what happens "When" Love brings Althea, and when the speaker lies "tangled in her hair," etc., etc.
When all these things take place, it as if the speaker is really free—freer than the birds that flit around in the air.
"Wanton" here a verb that here means to fly about (with the suggestion of aimlessness) or sport. It might also describe a person who is not faithful in their relationship. Still, we think the first definition here makes more sense, though the birds' actions are given a hint of romance with this second definition.
The speaker implies, in this first stanza, that one can be free even while in prison, if we have the power to use our imagination.