Marooned is a tiny poem about loneliness, and it gets its effect from how little it says. The speaker has a pint of wine, a small comfort, but no wife. The dash after "wife" leaves that absence hanging, as though the speaker can't quite finish the thought.
Then comes the comparison: he is "like a moth under / some high moon." A moth is drawn to light, and the moon is the biggest light in the night sky, but also a cold, distant one that can never be reached. The moth can only circle beneath it. That suggests a speaker who is restless and longing for something far out of reach, perhaps the wife, perhaps the company she stands for.
The title fits too. "Marooned" suggests being stranded, cut off from everyone else. The mood is quiet, wistful, and a little sad, but the image of the moth keeps it gentle rather than despairing.