Swansea Crown Court heard that Philip Cheetham, 48, started befriending the teenager last year using the MSN internet messenger service.
Her parents described her as a "quiet girl who spent a lot of time on her computer".
After building up the relationship on the internet he met up with her for sex in hotels such as the Dolphin and Dragon in Swansea and the Boar's Head in Carmarthen.
James Jenkins, prosecuting, said yesterday that when Cheetham started communicating with the girl last October he was already on a probation service led sex offenders' rehabilitation programme.
It was part of a three-year community treatment order imposed at Nottingham Crown Court in 2005 where Cheetham had admitted sexually grooming a 14-year-old girl from the city.
The court heard while he was arranging to meet the Swansea girl he was receiving daily "advice and guidance" from the those running the sex offenders' programme.
Cheetham was jailed for three years yesterday after admitting sexual activity with a child under 16 and the new offence of sexual grooming. Under the offence it is illegal for adults to meet or arrange to meet someone under 16 to engage in sexual activity.
Cheetham was told by Judge Michael Burr he could apply for parole within 18 months. However the judge emphasised release then would not be automatic and would only arrive when Cheetham could convince the parole board he was no longer a threat to young girls.
The Swansea offences came to light when the 15-year-old met Cheetham at a hotel telling her parents she was staying a friend. They found out it was not true and the police were called in.
The girl's parents found entries in her diary detailing sex with Cheetham.
Cheetham was arrested at Port Talbot station after the 15-year-old had left the train. He told police he was "in love" with the girl and claimed he did not realise she was only 15. However, police discovered he had bought her a child's railway ticket.
Patrick Griffiths, defending, said Cheetham's offending began after his marriage broke down. While what he did would "quite properly outrage decent-thinking people", no threats or force had been involved.Source:http://icwales.icnetwork.co.uk