Jeremy So, 32, pleaded guilty to one count of indecent assault of a person under 16 and five counts of sexual intercourse with a person over 14 under 16.
The girl he abused more than 12 years ago cannot be identified.
The pair were both promising classical musicians with the more-than-four-years-older So accompanying her for performance exams.
She watched the proceedings via video-link as Judge Andrew Scotting convicted So on Thursday, placing him on a three-year community corrections order requiring him to complete 275 hours of community service.
He was also ordered to undergo treatment and stay close to his parents' home.
So has "lost face" in the classical music industry he worked hard to establish himself in, the judge said, noting additional punishment due to media coverage of his case has "ostracised" him.
He now works as a data entrant at a pathology lab.
The girl is no longer pursuing her music career either, because she finds it too triggering.
The pair came into contact through social media when the girl sent a friend request to So, who was in year 12 at her school.
Teachers at the school expressed concern a few years later when So was tapped to teach classes of year seven and eight students, having observed their relationship, which was ongoing at the time.
Judge Scotting noted she was a "willing participant" in sexual conduct but could not consent due to her age.
"They were in a romantic relationship, both considered themselves to be in love and cared for each other," the judge said, noting there was no element of predatory conduct in So's offending.
Seven years after their relationship ended, in March 2021, So received a phone call from her.
She had reported to police two months earlier and they were recording the lengthy call when So admitted engaging in an unlawful relationship with a child.
He agreed he had pressured her to do things she was not comfortable with, describing some of the sexual contact as "horrible" and "terrible", apologising multiple times and saying he wished it had never happened.
Contemporaneous messages before the court showed So had attempted to end the relationship.
"He accepted he was corrupting the victim's childhood," the judge said on Thursday.
The judge accepted his contrition was genuine and said So was unlikely to reoffend.
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