The Beady Eye singer has had no contact with his wife of five years since it was claimed he had a secret seven-month old daughter with US journalist Liza Ghorbani, and his mother-in-law Mary Appleton is stunned by his cowardly behaviour.
She told Britain's Grazia magazine: "Liam hasn't bothered to call Nicole. He phoned her the day before it came out and he hasn't been in touch since. She can't get hold of him. She's absolutely devastated. This is so out of character for the Liam I know.
"Her sisters are supportive but she is in a terrible state. It's like he's lost his mind... it's been a real shock. It feels like he's been living a double life."
According to Mary, Nicole - who has 12-year-old son Gene with Liam - believes there is yet another woman involved, his former personal assistant Debbie Gwyther, who was fired the day after the news broke for being "too close" to the musician after photographs emerged of the pair lounging by a pool in Ibiza.
Mary added: "Nicole knows they are together. She has had it confirmed. We believe he's just dumped Nicole and gone... I believe he doesn't want to save the marriage."
Another source told LOOK magazine Nicole, 38, is unlikely to take Liam back because she feels "humiliated" by his betrayal.
They said: "I can't see her taking him back - not in a million years. I wouldn't be surprised if she sends him to live in his New York flat, where he can do what he likes with whoever he chooses - see if it makes him happy. A divorce would be hugely costly for him, too."