Demarcus Smith was 16 on the night he fatally shot Kemani Ridgeway in east Macon.
Now 17, Smith is beginning a 20-year prison sentence.
He pleaded guilty to voluntary manslaughter in Ridgeway's death during a Bibb County Superior Court hearing Monday.
Smith apologized to the members of Ridgeway's family present during the hearing, saying, "I'm sorry for what I've done."
Ridgeway's girlfriend told Bibb County deputies that Ridgeway argued with three males outside a vacant building in the 1900 block of Shurling Drive on Jan. 9, 2015.
Prosecutor John Regan said four shots were fired at Ridgeway, who was 20.
The fatal one struck him in the heart, he said.
Ridgeway's girlfriend drove him to a nearby gas station and called for help. He was pronounced dead at a local hospital about six hours later.
Smith was arrested that night and confessed to the shooting, Regan said.
In arguing for a bond to be set for Smith in October, defense attorney Alan Wheeler said Ridgeway and his client were both romantically involved with the same 19-year-old woman.
Monday, during the sentencing hearing, Wheeler said, "no matter what happened between he and Mr. Ridgeway, had he not had a pistol in his pocket the worst that would have happened would have been blood spilled because of a fight."
Information from Telegraph archives was used in this report. To contact writer Amy Leigh Womack, call 744-4398 and find her on Twitter@awomackmacon.