Barkin, 60, began dating Emmerson, 51, after meeting him at Hollywood star George Clooney's wedding to Amal Alamuddin last year in September, reported Us magazine.
"Ellen got swept up in the whole idea of Ben -- marrying a British lawyer, moving to London, living that life. Also, the idea of meeting him at George's wedding was so romantic," a source said.
The former couple got engaged on New Year's. Once the newness of the relationship wore off, however, Barkin realised she didn't know him well enough to marry him the source said.
This would have been Barkin's third marriage. She was previously wed to actor Gabriel Byrne from 1988 to 1999, and to billionaire Ronald O Perelman from 2000 to 2006.
She and Byrne had two kids together.