In 1828, while in Italy, he befriended Henry Wadsworth Longfellow and served as the aspiring poet's traveling companion; their friendship lasted 54 years.

In a letter of July 30, 1849, to Nicholas Brown, his successor as consul, Greene seems to imply that efforts were being made in Italy to annul his marriage; and in a postscript he refers to a rumor that Maria Carlotta died of a ‘putrid fever’ in Florence in May 1849 (MS, Brown University).

That Longfellow was deeply disturbed by the failure of this marriage is made clear by Greene in a letter to Sumner dated July 34, 1849: ‘I had some faint hope that he [Longfellow] might have written me – but I fear that the blow that has left me alone in the world – has broken the last tie between us.’ (MS Harvard College Library)."

Longfellow heard from his and Charles Sumner’s mutual friend "that Greene is engaged to Miss Porter of Providence, a girl of eighteen, with no dower but her beaux yeux."

He took up residence in East Greenwich once again in 1865; not long afterward he was chosen to represent the town in the Rhode Island General Assembly.

When he returned to East Greenwich, his good friend Longfellow purchased a home for him, which is still standing at 144 Division Street.