The pregnant former glamour model had her estranged husband undergo a polygraph to discover the extent of his extramarital activities following the revelation he had a seven-month affair with her pal Jane Pountney.
A source said: ''She called in private investigators to look into whether other stories about Kieran are going to come out and that's how he ended up taking a polygraph test. He failed, so she's telling him that she won't leave him if he tells her everything. She has been quizzing him non-stop.''
The 35-year-old star - who has 10-month-old son Jett with her husband, as well as three other kids from previous relationships - previously vowed to divorce Kieran, but she could now be changing her mind.
Kieran has reportedly moved back into the couple's £2.5 million home after Katie banished him to a log cabin in the garden.
The source added to heat magazine: ''He spent one night in the cabin, then was back in the spare room in the house the next day. Katie can't help it. She still loves him and she's six months pregnant with his baby. Plus she needs help with Jett.''
He also slapped a jet-lagged Taylor Hawkins.
The acclaimed performer had just cancelled touring due to a battle with cancer.