Inspiration, Borrowing, or Burglary?

“War poet Robert Graves 'stole work from his mistress'”

The article’s beginning:

Few would doubt the brilliance of Robert Graves, a man considered to be one of Britain's foremost war poets whose verses on Greek mythology and frontline conflict cemented his name in literary history.
        But one academic has accused the poet of stealing ideas, literary criticism and poetry from his one-time American mistress and passing them off as his own.
        Dr Mark Jacobs, a research fellow at Nottingham Trent University who has spent two decades studying 700 letters he received from Laura Riding Jackson as well as her literary works, said when she discovered the uncanny similarity in his texts she condemned her former lover as a "robber baron".

A quick link to a bio: Jacobs, Mark.