Personally, I think the painting aspect is simply a metaphor for how fixed but blurred memory becomes. To me, this is someone thinking about an old love, perhaps a first love, that is gone but has still left its mark on him. That mark is uncertain and rather unclear at this point, and is undoubtedly revised (like an antique etching glass design that somehow turned out wrong) and the narrator's awareness of the unreality of his memory makes it even worse, because he's ever more aware of the fallacy of his perspective, which helps make the memory fade and disappear even more.
Personally, I think the painting aspect is simply a metaphor for how fixed but blurred memory becomes. To me, this is someone thinking about an old love, perhaps a first love, that is gone but has still left its mark on him. That mark is uncertain and rather unclear at this point, and is undoubtedly revised (like an antique etching glass design that somehow turned out wrong) and the narrator's awareness of the unreality of his memory makes it even worse, because he's ever more aware of the fallacy of his perspective, which helps make the memory fade and disappear even more.