The pair had been in a relationship for two years, but had broken up.
The Crown alleges Ellis went to Ms Blackbourne's house and raped her, after she had ignored his text messages and had started a new sexual relationship with another man.
Ellis gave an account of "passionate'' and consensual sex with his ex-girlfriend, and said he visited that night with good intentions, said Justice Courtney.
The Crown alleges that Ellis stabbed the deceased with a knife he bought from home, and intended to kill her.
Ellis denies causing the fatal neck wound, and instead said the knife used to stab Ms Blackbourn was one that he'd bought, but she had at her house.
He said Ms Blackbourn had come at him with the knife, and after a struggle, she was stabbed in her upper body.
Both the Crown and defence agree that the neck wound was the fatal blow.
A witness gave evidence that Ellis was violent in a previous relationship, especially if he was feeling unwanted.
Justice Courtney said Ellis didn't accept the allegations, and denies strangling a partner in a former relationship.
The Judge also summed up a suicide letter Ellis wrote before attempting to take his life for the third time, while in custody.
The note said Ellis "had taken Ms Blackbourn's life not knowing what had come over him'', said Justice Courtney.
Ellis disputed the meaning he had intended to take his ex-girlfriend's life, instead saying he meant that if he hadn't visited Ms Blackbourn that night, she wouldn't have died.
The Crown alleged Ellis lied to neighbours and a friend about how the fire started.
Ellis' lawyers said he was was disoriented and traumatised about losing an ex-partner.
The jury members are considering the evidence.
