"The Idealist", by Arthur Machen

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Well, that's a weird story with rather an abrupt ending. But hopefully it's not to difficult to guess at what is going on... Why you'd write a story like that, however, if you are trying to be a respectable author, is difficult to understand. Hmmm...

From the annotations:

yahoos: in Part IV of Jonathan Swift's "Gulliver's Travels), Lemuel Gulliver encounters two races: the Houyhnhnms (intelligent, articulate horses) and the Yahoos (coarse, filthy humanoids). To Symonds, in other words, the other clerks are little better than subhuman brutes.

hoarding: a fence on which advertisements or bills are posted, or in this case the "icon" (meaning here, a portrait) of, apparently, a music-hall performer (prominent real-life women singers of the time included Marie Lloyd, Bessie Bellwood, and Jenny Hill).

And that's the way they do it ... taike the bun? Lyrics, apparently of Machen's invention, parodying a typical music-hall song in cockney dialect.

Ombres Chinoises: "Chinese shadows", a shadow-puppet show.

detached and semi-detached homes: a semi-detached house is one of a pair of single-family dwellings sharing a wall, as opposed to a stand-alone (detached) house.

entomologist: scientist who studies insects.

lay figure:a jointed wooden figure of the human body, used by artists as a model for the arrangement of draperies, posing, etc.

To follow along: https://en.m.wikisource.org/wiki/Ornaments_in_Jade/The_Idealist