The former glamour model was left devastated when her spouse slept with two of her friends, but he is now having treatment for sex addiction and she is confident he has changed his ways for good.
Chatting to Mark Dolan on Fubar radio, she said: ''Even my therapist said, 'Kate, there is no way he is ever going to cheat again.' It's really sunk into him. As long as he sticks to therapy and stuff.''
Katie - who has children Harvey, 12, Junior, nine, and Princess, seven, from previous relationships, and 11-month-old Jett with Kieran - admitted that she hadn't always fully understood that her husband was suffering from a real addiction.
She explained: ''I thought, 'no I don't believe it', it was just an excuse for someone to go out and s**g about basically, but then when you get a drug addict you know that they would do anything they can, you get people who will steal anything to pay for that drug they need that adrenaline.
''It's the same kind of thing with a sexual addict; they will risk everything. They will risk their family, their friends.''
And pregnant Katie also revealed that Kieran will have to see a therapist for the rest of his life to keep his addiction in check.
She shared: ''He is going to have to have therapy for the rest of his life. Even if it boils down to once every six months.
''It's nothing to be ashamed of.''
The '12 Years A Slave' director will receive the accolade at the London Film Festival in October.
Critics from all over the world were asked to name the best movie of the past 16 years.