The 46-year-old Christchurch labourer then went and stayed with a woman in Palmerston North last November.
Again, he proposed to her, before breaking her heart and taking off with a PlayStation, cellphone, tobacco and $120.
And on January 6 this year, at Waimate, he took 14 rings and a laptop valued at $10,000 from a third victim.
Police issued a plea for help in tracking Grogan down earlier this year and arrested him at a Christchurch mall after a tip-off from a member of the public.
At Christchurch District Court he earlier pleaded guilty to six charges of theft, unlawfully taking a motor vehicle, using a document for pecuniary advantage, and breach of a protection order.
Defence counsel Ruth Buddicom said Grogan had been lonely and depressed during this period while he had been estranged from his partner.
She claimed he regretted his actions and was genuinely apologetic.
Victim impact statements revealed a "severe" emotional toll, the court heard.
But while Ms Buddicom agreed they made for "quite harrowing reading", she claimed the statements needed to be put into context, in that meeting up with strangers the women had met online was "a very risky process".
Judge Tony Couch countered: "But that could be what lonely vulnerable people do."
The judge described the offending as "repeated cynical exploitation of vulnerable women".
One of the victim told how she had experienced tough times before Grogan came along where he treated her so well.
"It was amazing to have someone looking after me and considering my needs," the woman wrote in a victim impact statement.
"After he stole from me, I learned it was all a lie. It's been very upsetting and distressing for me."
She told of feeling foolish, hurt and angry, and now doubts whether she could ever trust a man enough to enter into another relationship in the future.
In jailing him for two years, four months and ordering him to repay $1800 in reparation, Judge Couch told Grogan in the dock: "You have hurt these women very badly."
