Jason O'Malley, 39, told the police that his girlfriend Kerry Sneddon liked him to apply "a little bit of pressure" and they had done it six or seven times in sex sessions although he didn't like doing it.
Sneddon's naked body was found at the home they shared in November last year.
O'Malley told the police that they had drunk beer and began kissing and stripping each other's clothes off after watching the X Factor. He said he remembered starting to have sex, but didn't recall the events leading to her death.
He is alleged to have throttled her after an argument, Sheffield Crown Court was told.
"The defendant killed Kerry Sneddon and when he strangled her he must have intended to kill her or at least cause her serious harm. We do not accept the defendant suffered genuine amnesia.
"We do not accept it may have been an accident during the course of some consensual sexual activity which is the suggestion he has made. A ligature was made and force applied for a considerable period of time," Prosecutor Bryan Cox was quoted as telling the jury.
O'Malley left his wife in July, 2007 and moved in with Sneddon. They lived at her home in Rotherham town centre. They had met on an dating site and begun a sexual relationship.
When Sneddon went on a holiday to Turkey, O'Malley met another woman on an internet dating site. They had a sexual relationship and she became pregnant.
Sneddon saw a copy of the baby scan in O'Malley's wallet, leading to friction between them, Cox said.