The relationship Justin Lee Collins had with a former girlfriend brought out the "demon" in him, a court has heard. St Albans Crown Court was played a secret recording made by Anna Larke in which he appears to verbally abuse her during an argument last July.
Prosecutor Peter Shaw said: "You are telling her there is something about this relationship, something about her that brings the demon out in you."
But Collins insisted the rant was completely out of character and it sounded "like someone else".
Comedian Justin Lee Collins and his ex-girlfriend Anna Larke, lived together from January to July last year in a deeply troubled relationship as she tried to overcome alcoholism, the court has heard.
Collins is accused of making her come off social networking websites, sleep facing him and throw away DVDs because they featured actors she found attractive.
Today he denied all those claims and denied making death threats against her.
Collins said such was his former girlfriend's jealousy that, as soon as his appearance in the West End production Rock Of Ages was announced last year, she immediately accused him of having an affair with fellow performers.
He said: "Far from being excited for me or being happy about the prospect, she was on the computer to look at the cast list.
"This was before I had even started rehearsing or met the cast.
"Anna knew their names and was confronting me with the better looking members of the cast, asking 'Which one is it going to be?"'
Collins said the seven-month relationship with Ms Larke was "absolute hell".
"I thought she loved me and was crazy about me," he said, "but it turned out only the second part was true."
This afternoon the prosecution case closed and Collins entered the witness box to begin his defence.
Wearing jeans and a dark jacket, the father of two admitted to meeting Ms Larke in 2006 and beginning what his barrister Sonia Woodley QC called "a liaison" in June 2007.
In November 2008 he was warned that news of his cheating would be published in the tabloids but he did not know which women would feature.
He said he confessed everything to his wife Karen, mother of his two sons and they decided to stay together.
He said Ms Larke did not take the news well that they could not see each other again.
He said during the next two years she continued to contact him and blackmailed him, threatening to go to the press with her story.