"Her injuries required stitches, you perforated her bowel and the injuries were described as potentially life-threatening," Judge Coyle said.
Gates also stabbed a man in the arm, who required stitches.
Gates then took a Remington semi-automatic rifle and went to his parents' house to confront his father, whom Gates blamed for many of his problems.
He returned home and found the Armed Offenders Squad waiting.
After an hour-long standoff, Gates surrendered and police searched the property, finding a significant amount of ammunition, 17 cannabis plants, seedlings and dried cannabis.
Gates admitted the cannabis was for personal use and that he sold a small amount to friends and family, about $100 worth a week or an estimated $30,000 in total.
Judge Coyle said there had been no lasting effects on Gates' victims, who bore "no ill will" towards him. He cited a psychological report into Gates' mental state that found he had a "difficult background".
"Your childhood was characterised by violence and alcohol abuse. You seemed to have been raised by a parental structure which, instead of nurturing and fostering good relationships, instead of cherishing you, repeatedly belittled and demeaned you ... With that background, you found yourself in recent years facing extreme financial pressure and bankruptcy."
Judge Coyle said the report described Gates as a proud man who was distressed and humiliated by not being able to provide for his family.
"On the night of the offending, you simply lost control and snapped ... you erupted in violence against those closest to you, in particular, your partner."
Judge Coyle said Gates then "lost all hope" and brandished a gun in the hope that police would "end it for you and shoot you".
When sentencing Gates, Judge Coyle spoke of the country's appalling record with violent crimes and the need to send the message to the community that violence in any context was unacceptable.
"Mr Gates, there are many people in society that have had as bad a start to life as you that don't respond with violence.
"Your circumstances provide a powerful explanation, but they do not provide an excuse.
There can never be an excuse for the type of violence you meted out to those who love you.
"But for a matter of millimetres, you could have inflicted life-threatening injuries."
Upon sentencing Gates to four years and one month imprisonment, and a warning under the three strikes law, Judge Coyle said these events should show Gates "You can bottle up your emotions for a time but, in time, they explode."