The man, 42, pleaded guilty in the County Court to two counts of grooming a child under 16 for sex.
The man, who was aged 36 to 38 at the time, started messaging the teenager in June 2017 when she was 13.
At the time, the man was in a relationship with the girl’s mother, who believed she was engaged to him, and the girl thought of him as her stepfather.
However, the pair knew him under a false name.
The court heard the man sent sexually explicit messages to the girl between June 2017 and October 2019, ultimately seeking to have sex with her.
The man and the victim exchanged thousands of messages over Snapchat between June 2017 and October 2019 while the girl was aged 13 to 15, with half being sexual in nature.
Among the messages were requests that she have sex with him so she could have a baby for her mother and the man, who were unable to conceive.
He also asked the girl to masturbate herself while on the phone with him.
The court was told the man was eventually caught after the girl confided in a teacher, who alerted the authorities.
In a police interview, the man denied knowing of the name he had told the pair his name was, and denied conversations about having a child with the girl.
He was also in a 10-year de facto relationship with another woman.
In his sentencing, Judge Marcus Dempsey spoke of how the man had had “a rough patch” with his partner for four or five months and it was during this time the man started talking to the girl’s mother.
However, the man said he had not been in a relationship with the woman.
Judge Dempsey described the offending as a “gross breach of trust”.
“There was no question you knew her age and no ambiguity she viewed you as a stepfather,” he said.
The judge also noted the man’s risk of repeating the offending “was low” and that the man had been charged with two charges instead of one because there was a change to the legislation during the offending period, otherwise he would have faced only one charge.
The man was sentenced to four years and two months in prison.
He has to serve two years and six months before he is eligible for parole.
The judge ruled that the 64 days he has spent in pre-sentence detention be counted as time already served.