I really only know what I've already said- that John Tann left his family by 1865. Transcript of the newspaper report is thus:
Bury and Norwich Post Tuesday 3rd August 1869
Bigamy by a Norwich Man
At the Huntingdon Assizes on Tuesday, John Tann 51, carpenter, was indicted for bigamy at Stansground on 19th Feb.1868.
William Futter said he lived at Norwich and was present at the marriage of the prisoner to his first wife, Hannah Maria Futter,which took place at St Lawrence Norwich 15th Nov.1840.
Witness Charles Tann son of prisoner, said his father left Norwich about three years ago and at that time asked the witness
how his mother was, and how all the children were. He told him his mother was quite well, that his brother was dead, and the others were middling. His father said he was happy and comfortable, had a good situation, and was in receipt of good wages.
He remembered his father being committed to prison, to keep the peace towards his mother, by whom the present prosecution was instituted.
The parish clerk of Stansground proved a second marriage between prisoner and Lucy Brain (widow) in Feb.1868, and the Jury,
having found the prisoner guilty was sentenced to five mths imprisonment.
The brother referred to died in 1865 so presumably John Tann had left the family by then. Charles himself died in 1871.
John Tann was still alive in 1889 when Hannah herself was charged with bigamy. He was living in Marlingford, apart from his second wife Lucy and children who were in Gateley. I only have a record of Hannah's acquittal, no details of who brought the prosecution. Either it was John Tann who fancied his chances a second time, or, more likely perhaps, it was Robert Eagleton who didn't know about her past.
Either way, since she was acquitted and since husbands 2 and 3 were dead, her marriage to Robert Eagleton was presumably lawful it being 20 years since John Tann had left her. (Marriage 2 was at least 9 years after he'd left. )