Three short lines set a whole scene: a pool hall with almost no one in it. The speaker and a bartender are the only two people there. That's all we're told, and the poem's power comes from how much it leaves unsaid.
The speaker never says "I'm lonely," but the details point that way. A pool hall is usually a place for company, noise, and games played against other people. Here it's quiet and nearly empty. The phrase "Me and a bartender" sounds casual, almost flat, as if the speaker is shrugging. Yet the bartender is described only by job, not as a friend or even a name, which suggests a closeness that's really just proximity. They share a space, not a conversation, at least as far as the poem shows.
The mood is quiet, a little wistful, and slightly deadpan. It could be peaceful solitude or low-key isolation. The poem lets us decide, and that ambiguity is what lingers.