Chan Kang-kwong lived a quiet life with his wife in Tuen Mun before she encountered the Church of Almighty God, which has been branded an "evil cult" and banned by Beijing.
As his wife became more involved in the church, also known as Lightning of the East and which has one million followers on the mainland, Chan became more worried.
"She was addicted to the heresy of the Church of Almighty God," said Chan, 55, who works at a financial company. "It was very serious. Her conversion influenced me a lot. I couldn't sleep for a whole week at that time. And our relationship was very bad."
The sect, which believes a mainland woman is the second coming of Jesus Christ and calls the Communist Party the "great red dragon", is notorious among Christian communities for its aggressive recruiting methods.
Hong Kong's mainstream Christian churches have given sermons, handed out leaflets and set up a Facebook page to warn people about the sect.
It allegedly has kidnapped, tortured and brainwashed people into converting on the mainland. In December, about 1,000 followers were arrested and accused of spreading doomsday rumours, a key religious concept of the sect.
Mainland immigrants brought the church to Hong Kong about 10 years ago, and there has been a huge push to expand membership beyond its 2,000 followers, said Kevin Yeung Tze-chung, general secretary of the Concern Group on Newly Emerged Religions, who has been studying the sect since 2008. He said the source of money spent on the campaign was unknown.
The Church of Almighty God's "belief is antisocial and destroys the value of family", Yeung said, adding that the sect denies the value of love, care and tolerance and keeps indoctrinating followers with its second-coming story. Yeung claims 200 Christians in Hong Kong have been harassed and "mentally hurt" by the sect.
Saleswoman Leung Fung-tai, 50, of Tin Shui Wai, said she had been targeted by the sect and dragged to a Bible study group by an acquaintance.
She was told bad things would happen to nonbelievers and she stopped attending the group because she did not like being threatened.
Chan's wife, 52, finally returned to her regular church and refuses to talk about her experience because she feels guilty and ashamed.
But others have been strongly influenced by the sect.
Angel Lee's mother has been a member for more than a year. Lee, 28, said her and her sister's relationship with their mother had soured. She had become irritable and spent all day and much of the night at the church. She had also ignored all her old friends.
Kung Lap-yan, an associate professor studying religion at the Chinese University of Hong Kong, said he preferred to call the church a "new religion" rather than a cult.
Mainstream churches were afraid of losing their followers.
"I don't see any bad influence it has had," he said. "Every religion has the freedom to preach and there is no evidence it has done anything illegal."
The Church of Almighty God refused to directly comment on the accusations, but hit back at its critics.
"Mainstream religious leaders don't serve God. Instead, they serve themselves. They make themselves the idol of their followers and control them," it said in a 40-page statement.