The speaker looks back at the past and admits it doesn't hold up very well. We like to remember it as beautiful, but there's "little to sustain" that picture. We either bury it, pushing it out of mind, or go over it again with strangers across a drink. Those listeners don't know the full story and will forget it soon, so the retelling feels a little hollow.
The second stanza turns to a blunt conclusion. People judge themselves, and nobody really learns from what others have lived through. So teaching, the passing on of hard-won lessons, "hardly helps." The poem ends right there, with no comfort added.
The mood is quiet, tired and resigned. The speaker doesn't sound angry, just worn down by a plain truth. The short, plain lines and the casual setting of a drink with strangers make the disappointment feel ordinary, something the speaker has simply come to accept.