A Melbourne ice addict who said did not know his gun was loaded when he pointed it at his girlfriend and fired has been found guilty of manslaughter.

Nelson Lai, 35, was acquitted of murder after fatally shooting 22-year-old Rekiah O'Donnell in his Sunshine home in October 2013.

Lai claimed he was looking after the gun for drug dealers and did not know it was loaded.

The court heard how Lai and Ms O'Donnell had a violent and volatile relationship, with the 22-year-old subject to constant abuse as well as threatening and controlling behaviour.

The pair had met in a furniture store and became friends on Facebook. Their 14-month relationship was characterised by abuse and suspicion.

After one assault, Ms O'Donnell told a friend via text message "I know it's my fault for not escaping earlier but I was naive. He forcibly grabbed me last night to get my phone. I was so scared".

Lai's paranoia and possessiveness continued, fuelled by the drug ice, texting her in the days before her death "your phone bill will cost you your life" and "you're dead".

Lai told the jury last week the couple, who were both users of the drug ice, were "kicking back in my room" when he reached behind his bedhead and picked up the gun.

Nelson Lai has been found guilty of manslaughter after shooting his girlfriend. (9NEWS) (9NEWS)

Lai was sitting up in bed, with Ms O'Donnell to his left, when he started playing with the gun and pulling the trigger.

"I mean, I'm not sure how many times because I wasn't counting it," he said.

"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---' really loud and probably some other things.

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

Lai said he called Triple Zero and attempted to stop the bleeding, and performed CPR when Ms O'Donnell stopped breathing.

Prosecution lawyers said on the day of Ms O'Donnell's death, Lai's blood was boiling because he suspected cheating, and deliberately shot her in the temple.

But defence lawyers successfully argued that the triple zero call showed Lai did not mean to kill.

Ms O'Donnell's family left the court crying, her mother Kerryn Robertson telling 9NEWS they were "devastated" and "a bit lost for words".