It's highly likely that this (alleged relationship) with a woman in England, was just another example of Simonides using someone for money and free accommodation (freeloading). He likely lead this possibly ugly and possibly desperate, yet probably rich woman, on. Playing on her loneliness with his sleezy charms. In other words, a sham and for show.
I wonder why his engagement failed. May be because he had no money and no prospects. Looks like that was the reason he left England. No further info from Pinto:
"The last dated document from England is a letter from Liverpool of March 31, 1865, in which he wrote about his plans to marry an English woman, named Miss Morland." Simonides in England," p.123 A Forger’s Progress/Pasquale Massimo Pinto in Die getäuschte Wissenschaft
Ein Genie betrügt Europa – Konstantinos Simonides (2017) Andreas E. Müller / Lilia Diamantopoulou / Christian Gastgeber / Athanasia Katsiakiori-
Rankl (Hg.)
Also from Pinto:
[The reconstruction of Simonides’ years in Victorian England relies first of all
on a number of unpublished manuscript documents, the most important of
which are the letters to, from and about Simonides included in the manuscript
Additional 42502AB of the British Library and originally from the personal
archive of John Eliot Hodgkin, probably Simonides’ chief patron in England. The
papers of the book-collector Thomas Phillipps and the librarian Frederick
Madden that are in the British Library and the Bodleian Library of Oxford, also
deserve to be mentioned. Next is the information that can be collected from what
Simonides himself wrote both in the prefaces of the works published in England,
such as the Facsimiles of certain Portions of the Gospel of St. Matthew etc. (1861)
or The Periplus of Hannon (1864), and in newspapers. Finally, at least three
scholarly contributions must be taken into consideration: a chapter included by
the amateur historian James Anson Farrer in his 1907 book on Literary Forgeries,
based on the papers of Hodgkin; the substantial chapter devoted to Simonides by
the book scholar Alan N.L. Munby in his stunning work on Thomas Phillipps,
published in the 1950s (the “Phillipps Studies”); and the book about the Codex
Sinaiticus and the Simonides affair written by the New Testament scholar James
K. Elliott in 1982]
[On his (first) arrival (in England) he was undoubtedly welcomed by the long-established Greek
merchant communities of Liverpool and Manchester, from whom he first re-
ceived material help and practical support, as he later acknowledged in his Fac-
similes: ‘my compatriots, the Greek residents in Liverpool and Manchester, to
whom I return my sincere thanks for their friendly sentiments and their many
kindnesses’. A few names stand out here and there in the pages of his works:
Stamatis Frangopoulos, Constantinos Pappas, and above all Demetrios Rho-
dokanakis.]