Hamilton was killed on May 18, 2019, the day he and Simeon's baby daughter turned 1 year old.
The pair had been dating for about four years. Simeon was 18. Both attended a house party in Mt Roskill the evening before Hamilton died.
Jurors heard outbursts of violence and arguments typified the relationship.
Lummis said further angst in May 2019 emerged from financial issues and Simeon's changing mood.
Lummis reminded jurors of a local shopkeeper's testimony that Simeon's mood darkened in the weeks before Hamilton died.
The prosecutor also mentioned evidence a witness gave about Simeon's mother being the victim of the teenager's violence.
Jurors heard Simeon was once accused of "pummelling" her mother, smashing her in the face before Hamilton forcefully intervened.
"She punches her own mother in the head repeatedly ... all around some sort of allegation of jealousy."
Lummis said Hamilton told a Dominion Rd neighbour he was deeply unhappy in the relationship, and if he was home five minutes late, Simeon would accuse him of infidelity.
She told jurors some mystery remained about events in the couple's flat the night Hamilton was killed.
But she said Simeon clearly grabbed a 30cm kitchen knife and stabbed her boyfriend in the throat.
"We know she didn't hang around for too long. We know that he took his last breaths and died on the kitchen floor."
"When you look at the choice of weapon ... it's hardly surprising that the result was fatal."
Lummis described Simeon's actions as "maximum destruction with minimal effort, leaving him to die".
She said no evidence existed of a struggle, the killing was at the very least reckless, and Hamilton was found with no defensive wounds.
"Mr Hamilton didn't see that knife coming."
She urged jurors to contextualise any of Simeon's apparent or real contrition.
"It's murder even if later you're sorry and regretful."
Jurors were reminded of pathologists, police and partygoers who gave evidence.
One party guest said he was "pissed when he got there and pissed when he left" so his testimony was of limited use, Lummis said.
Another started drinking at 10am and consumed methamphetamine that day as well.
Defence counsel Paul Borich QC said the couple's relationship tensions cut both ways.
"Brendon was angry and drunk at the party."
Borich said a fuse of fury was possibly lit at the party, where some witnesses described Hamilton as aggressive.
"According to his friend, he was as angry as he had ever seen him."
Borich asked jurors to imagine if roles were reversed - and Hamilton was on trial for murder.
"Imagine how the Crown would be highlighting to you Brendon's drunkenness ... how upset he was about the lack of money, how upset he was he couldn't have baby with them."
The young parent's daughter was living with her paternal grandmother in Rotorua.
Borich said the Crown called highly educated forensic witnesses who failed to say anything meaningful about what happened in the moments before Hamilton was killed.
"The Crown has attempted to build its case on guesswork."
Borich suggested Hamilton was spoiling for a fight in the small kitchen, leaving Simeon with few options.
Borich said jurors would have to set aside sensitivities about speaking ill of the dead, and recognise Hamilton had two sides to his character - one lovable, the other violent.
Justice Neil Campbell is expected to sum up the case to jurors tomorrow morning.
Jurors are then expected to retire and consider their verdict.
