::I count 10 references to the question of a formal marriage in the one paragraph.  I might revise as follows (sorry  I don't know how to do strikeouts, or I would use them, for the ease of comprehension of my proposed changes): 
 ::. . . Fuller and Ossoli moved in together in Florence, Italy.  At least originally, Fuller balked at marrying, in part because of their different religions; she was Protestant and he was Roman Catholic.  Emerson speculated that the couple was "married perhaps in Oct. Nov. or Dec" of 1847, though he did not explain his reasoning.  Biographers have speculated that the couple married on April 4, 1848, to celebrate the anniversary of their first meeting.  [Note from me:  Having been acquainted for a year seems a weird and flimsy basis for speculating that a couple got married, and unless this is elucidated, I would delete the sentence.]  By the time the couple moved to Florence, they were referred to as husband and wife, though it seems certain that at the time their child was born, they were not married. [Note from me:  Why does it seem certain?  Without an explanation, it's confusing, and I would take out the last part of that sentence.]  By New Year's Day 1848, Fuller suspected that she was pregnant but kept it from Ossoli for several weeks.  Their child, Angelo Eugene Philip Ossoli, was born in early September 1848; they nicknamed him Angelino. The couple was very secretive about their relationship but, after Angelino suffered an unnamed illness, they became closer.  [Note from me:  Why does being secretive about their relationship relate in a contradictory way ("but") to their becoming closer?]  Fuller finally informed her mother about Ossoli and Angelino in August 1849. The letter explained that she had kept silent so as not to upset her, "but it has become necessary, on account of the child, for us to live publicly and permanently together."  Her mother's response makes it clear that she was aware that a legal marriage had not taken place.  [Note from me:  If the mother was "aware," that tells me that the question of a marriage was resolved.  If it was not resolved, the sentence should read, "makes it clear that she understood that a legal marriage had not taken place.]  Even so, she was happy for her daughter, writing: "I send my first kiss with my fervent blessing to my grandson."  Modern biographers are still unclear if Fuller and Ossoli ever married.  [Note from me:  This last sentence seems superfluous; even after my suggested deletions, it's clear from the preceding text.] 
 ::Thanks, Midnightdreary, for working with me on this.  I look forward to seeing what you think.