So, we'll go no more a-roving
So late into the night,
Though the heart be still as loving,
And the moon be still as bright.
The “So” that begins the opening line points to questions relating to the  refrain , ‘go a-roving’, that lie at the heart of this poem.  Assonant  “o"s in the opening line creates moaning effect, impl poet is weary 
 What is the circumstance that has led to the proclamation that they will “go no more a-roving”? The poem is a response to over-indulgence. The tone can be read as morose or self-mocking or mock-serious. Or just the usual regrets the morning after the night before! 
 Byron’s biography explains the circumstances which conceived this poem. He was a relatively young man, having just turned  twenty-nine , and fond of drink and women.   Feeling the ill effects of his night out he melodramatically declares that he and his companion will no longer continue with reckless over-indulgence.
So well go no more a-roving