So, we'll go no more a roving So late into the night,
The speaker opens with some anaphora, repeating the same structure to begin each line: "so we'll go no more a roving / So late into the night." The word "rove" means "wander" or "roam."
The speaker is saying that it's time stop wandering around aimlessly late into the night. It's also possible that he (and we just assume that it's a "he") is being metaphorical. What, really?
Really. Byron wrote this poem when he was 29, and even at that very young age he felt that he was getting old, maybe like this guy. (Byron would, in fact, die just seven years later.)
By saying "we'll go no more a roving," he could be saying his life is drawing to a close, that the time for play is over, and that he must prepare for old age and death.
There's a "we," so it's possible the speaker is talking to somebody else (a buddy, a girlfriend). He could also just be saying "we" to mean himself—people do that sometimes.
Though the heart be still as loving, And the moon be still as bright.
The speaker says they'll go no more a roving, even though the moon is still as bright, and the heart is "still as loving."
The point is that even though the heart is very much alive, very much emotionally ready to go rove ("loving"), and even though the moon is still really bright (meaning they can wander around and still be able to see), it's time to stop.
Well why stop roving when the heart still wants to, and the bright moon is very inviting? Probably because there comes a time when you have to stop wandering and messing around.
This is a way of saying one must stop messing around and playing and grow up. It also, very subtly, is a way of alluding to the approach of death.
Sure, the poem doesn't really talk a lot about death per se, but fears of getting old and fears of "roving" too much sound like the fears of somebody whose life is nearing its conclusion.
While the word "still" means "continuous" or "continually," we can't help thinking of "still" in the sense of "not moving"—i.e., the stillness of a dead body.
It doesn't look like it, but "roving" and "loving" rhyme (play around with the pronunciation until you find one that suits you). "Night" and "bright" rhyme as well, which means the rhyme scheme for this first stanza is ABAB.
We'd love to tell you about the meter, too, but it's a little tricky. For now, keep in mind that it is a version of trimeter (meaning there are three beats per line). Head over to "Form and Meter" for a more thorough rove through this poem's metrical and rhyming nuances.