Nelson Lai, 35, who claimed he did not know the gun was loaded when he pulled the trigger and killed Rekiah O'Donnell, 22, was found guilty of manslaughter, not murder, by a Supreme Court jury.

Justice Michael Croucher on Friday said he could not exclude the possibility Lai was telling the truth when he claimed he had not been arguing with Ms O'Donnell before the shooting, was not looking where he was pointing the gun, and it was just a tragic accident.

Justice Croucher said while Lai's history of abuse towards Ms O'Donnell had been "appalling", there was no evidence he had threatened her on the morning she died.

The judge praised Ms O'Donnell's mother, Kerryn Robertson, for her courage when turning to Lai during an earlier pre-sentence hearing and telling him she forgave him.

Justice Croucher did not think many people, including himself, could forgive their child's killer.

Lai, who was found guilty of manslaughter after a jury deliberated for 1½ days following a 17-day trial, was jailed for nine years and five months with a non-parole period of six years and 11 months.

During his closing address to the jury, Crown prosecutor Andrew Grant claimed Lai had been angry with Ms O'Donnell when he shot her.

"He believed she'd been unfaithful and was planning to end their relationship," Mr Grant said.

"He was jealous and possessive of Ms O'Donnell and he'd regularly acted in a threatening, controlling and violent manner."

Mr Grant said the Crown case was that on October 11, 2013, Lai snapped in the bedroom of his Sunshine North home and was in a rage when he shot Ms O'Donnell in the temple at about 9am.

Ms O'Donnell, a regular ice user, had previously told a girlfriend she was done with Lai and had read psychology books to work out why she kept going back to an abusive relationship.

In one text sent to Lai on November 27, 2012, Ms O'Donnell said: "Every time you abuse me or make a mistake I forgive you. I run back to your side. No matter how much you've brought me down I'm always there trying to lift you up, encourage you no matter how many times you scream at me, threaten me, hit me, lie to me or break my items. I've stuck by you and continue to try my best to please you without giving up everything I am."

In text messages sent by Lai to Ms O'Donnell on August 20, 2013, he said: "Block me and you'll see what happens. I dare you to give me a reason to end this miserable life here ... I hate lying dogs more than anything, K, dog. Call me if you're not lying. It's been one day and you're already with some other c--t". "Coming for you, lying dog, you'll see. I know where your mum's house is, you f--king cheating dog rat. Swear on my life you've got 10 minutes to call me ... this time you've gone too far. I will end both our suffering ASAP. F--king dog rat, stop lying."

Lai, who has previous convictions for attacking his former partner and the mother of his two children, told the jury he had loved Ms O'Donnell and did not know the gun was loaded when he accidentally shot her.

He had reached behind his bedhead and grabbed the gun and started pulling the trigger.

"We were both sitting on the bed at that time, and then she got up to do something ...

"Then the gun went off and I heard a thump on the ground, so I crawled over to the edge of my bed and saw her laying there on the floor. I saw her holding her head and I yelled out, 'F--k' really loud and probably some other things.

"Next thing I know was my parents standing at my door with the door open."

Lai called triple 0 and told the operator he had accidentally shot his girlfriend before trying to revive her.