Mr Charmley has been minister for the two parishes, as well as Torteval and St Saviour's, since 2013, with his wife supporting him as assistant priest, as part of a new four-parish plurality.
But a shortage of staff meant the system did not work and will come to an end later this year.
A special service will be held on 30 October to mark the end of the four-parish experiment.
When Mr Charmley was interviewed for the post in 2009, it was understood he would take on Forest and St Saviour's, and eventually Torteval and St Peter's, when the Rev. Maurice Strike retired.
He was to be supported by three or four non-paid clergy.
'At the time there were four licensed lay ministers, so there was already staff in place,' he said.
The couple have two children –15-year-old Jonathan and 13-year-old Sophie – and Mr Charmley said they had been missing out on spending time with their children, as well as aspects of church work, such as visiting people, reading theology and having time to pray.
