Sheehan (24), from Laois, played the lover of single mum-of-two Gemma Jones in the BBC programme.
However, the show, which aired at 9.30pm on Fridays, was dropped after just six episodes -- despite being heavily promoted by the broadcaster.
It drew average audiences of 2.5 million, but the final offering was watched by a meagre 1.72 million viewers.
Fans of the show commiserated with writer Oriane Messina, who admitted the BBC is "a tough nut to crack". "We just didn't get the ratings we needed," she wrote on Twitter.
Despite the setback, Sheehan won't be short of work as he still has a busy schedule ahead of him next year.
Love/Hate is due to return for a fourth series and his first Hollywood film is to be released.
The film, The Mortal Instruments, in which he appears alongside fellow Irishmen Jonathan Rhys Meyers and The Hobbit star Aiden Turner, could act as a springboard to launch his US career. Set in New York, the vampire flick follows a teenager who discovers she is the descendant of a line of so-called Shadowhunters who battle to protect the world from demons.