Jamelah Asmar - who used to be Katie's best friend and claims she kissed Peter last year - says he still hasn't moved on from his 2009 divorce.
She told Now magazine: ''Well, Pete definitely isn't himself. He knows exactly why they separated and it's a very good reason but he won't reveal it because of the kids. He's still got demons in his head, he's never going to get over it. Pete's an utterly broken man.
''She can get him like that [clicks fingers]. All she has to do is text. He'll be all happy and bubbly and then the phone will go and everyone will be like: 'Oh no, we've lost him'.
''He was even getting messages from her on Christmas Day in 2010 - she wouldn't leave off.''
Katie, 33 - who has kids Harvey, Junior and Princess with the 'Mysterious Girl' singer - has since gone on to marry and divorce cage fighter Alex Reid.
Pete, however, has previously opened up about his struggles start a new life.
Appearing on 'Piers Morgan's Life Stories' he explained: ''I finally found happiness (with Katie), it was the first time I'd felt good.
''I felt good about everything. I think that's probably why I've never been able to (move on) ... I've moved on in leaps and bounds in one way but in another way I'm still a bit tortured inside.''