Collins was caught in an undercover police operation this year but the sentence also relates to 2011 offending against a girl who was 15 at the time.
The 2011 offences involved a girl he had met on an online dating site and with whom he had exchanged messages and photographs.
He later met and sat with the girl in a vehicle where Judge Josephine Bouchier said "there was touching going on but not of a particularly criminal sort".
When the girl turned 16 Collins met her again at a hotel and performed oral sex on her.
The second lot of offending happened this year when an undercover police agent set up an online profile posing as a 13-year-old girl.
Collins talked with the fictitious girl for six weeks, including conversations about masturbation, showed her photos of himself dressed in underwear and suggested meeting.
The "girl" mentioned her age five times through the conversations, but when she mentioned she would be in Palmerston North, Collins suggested they meet up. The meeting never occurred, however.
At sentencing in Whanganui District Court last week, Crown lawyer Chris Wilkinson-Smith argued for Collins to be added to the Child Sex Offender Register so he could be monitored post-sentence but this was declined by Judge Bouchier.
Mr Wilkinson-Smith said Collins' risk profile "must be significant".
"As recently as June this year he was trying to build relationships for a sexual purpose," Mr Wilkinson-Smith told the court.
Defence lawyer Roger Crowley argued his client's actions since his arrest demonstrated he was no longer a risk.
"He engaged in counselling on day one; he was said to have real palpable remorse."
A pre-sentence report assessed Collins as being "low risk of further sexual offending".
Mr Crowley said Collins had lost everything.
"It's a tremendous fall from grace from a man who has led a blameless life," he said.
"He has lost his self-respect, his marriage, any contact with his children, his career, his social status and his ability to function in the community properly because of this offending."
Judge Bouchier said aggravating factors included the vulnerability of the victims, the pre-meditation and the length of time the second offending took place.
"I accept that his remorse is genuine and not situational, as in for himself," she said.
On top of the home detention Collins was ordered not to associate with or contact the victim, anyone under the age of 16 or use any device that could connect to the internet.
Yesterday, Whanganui Girls' College issued a statement confirming that the case did not involve any student at the school, and that Collins was immediately placed on leave once the allegations were made. He later resigned.
"Throughout the investigation and courts process, we have worked closely with the police, Ministry of Education and New Zealand School Trustees Association to ensure that at all times we handled this matter well for our students and school community and in line with best practice."
-Wanganui Chronicle
