Perhaps some general context is not wholly irrelevant here. Before the
end of the 19th-c homosexuality did not exist. The act of sodomy
existed, with a death penalty attached to it incidentally. And that act
was equally condemned whether performed by two men or by a man and a
woman. (Note I do not use the word heterosexual here, because that
didn't exist before the end of the 19th-c. Performance of the act of
sodomy was no indication whatever of what we now refer to as a person's
sexuality. Consider the following two texts, one from around 1680, the
other around 1815.

>From "The Imperfect Enjoyment" 
John Wilmot, Earl of Rochester

Ev'n her fair hand, which might bid heat return
To frozen age, and make cold hermits burn,
Applied to my dead cinder, warms no more
Than fire to ashes could past flames restore.
Trembling, confused, despairing, limber, dry,
A wishing, weak, unmoving lump I lie.
This dart of love, whose piercing point, oft tried,
With virgin blood ten thousand maids have dyed
Which nature still directed with such art
That it through every cunt reached every heart -
Stiffly resolved, 'twould carelessly invade
Woman or man, nor aught its fury stayed:
Where'er it pierced, a cunt it found or made -
Now languid lies in this unhappy hour,
Shrunk up and sapless like a withered flowe


"Do you know anything of my cousin's captain?" said Edmund; "Captain
Marshall?  You have a large acquaintance in the navy, I conclude?"

"Among admirals, large enough; but," with an air of grandeur, "we know
very little of the inferior ranks.  Post-captains may be very good sort
of men, but they do not belong to _us_.  Of various admirals I could
tell you a great deal:  of them and their flags, and the gradation of
their pay, and their bickerings and jealousies.  But, in general, I can
assure you that they are all passed over, and all very ill used. 
Certainly, my home at my uncle's brought me acquainted with a circle of
admirals.  Of _Rears_ and _Vices_ I saw enough.  Now do not be
suspecting me of a pun, I entreat."

Edmund again felt grave, and only replied, "It is a noble profession."
                (_Mansfield Park_, Ch. 6)

For those with stereotyped notions of Jane Austen -- Did Jane Austen
really mean that? Yes she very definitely did. Nor did Rochester link
sodomy with any indication of one's "sexuality."

The same trends in psychology that Nancy traces as well as the writings
(and actions) of such men as Oscar Wilde _created_ homosexuality_ and
thus _heterosexuality_. All this happened nearly within Eliot's lifetime
-- and though lesbian and gay novels were appearing by the 1920s the
cultural 'event' was recent enough to make the categories a bit strange.
Mr. Eugenides may (a) desire to engate in sodomy with the narrator and
(b) not be a "homosexuall."

This may or may not color the episode in TWL.