The illustrations, of course, are the key to the code. You decipher what you can. The Illuminated Gentleman had a lover (here is an illustration of a pierced heart) who descended to the Neath. A painful period of separation.
So when the Gentleman's superior (represented by a snow-laden tree) offered him a task in the Neath, the Gentleman accepted. The task was not kind: the design, here, is a sword impaling a hart.
But when the Gentleman descended, an unfortunate realisation. Two illustrations become one. The target (the hart) and the lover (the heart) were one and the same.
The last line is uncoded. 'Tomorrow, I do my duty. Tonight, I seek the irrigo blessings of St Joshua, so that I might do so in ignorance. I will not remember this confession, nor my beloved.'