(newsoftheworld.co.uk) - Kevin Federline, who is battling for custody of their two boys, said: "Britney's behaviour has already put our kids at risk and I can't let things get any worse.
"She's lost all grasp on reality and is dragging the children through hell. Her mood swings are now so wild that I live in fear of getting a call telling me that she has killed herself.
"I can't allow her to have custody because I seriously believe she could harm our sons. I've shared her life and I know she's capable of anything with pills and a few drinks inside her."
Kevin has never spoken publicly about Britney, 25. But he confided his secret worries in emotional conversations with girlfriend Nicole Narain. She told the News of the World how he:
CAUGHT Britney breast-feeding son Jayden, one, while DRUNK on vodka.
FEARS her wild and erratic behaviour has "damaged" Jayden and two-year-old Sean.
WARNED her to stop leaving the kids alone by the pool and driving them in the car without seatbelts.
REALISED Britney is BISEXUAL after she made a pass at Nicole in a loo.
In a rare and remarkable insight into the troubled star's life, Nicole, 33, revealed it was the breast-feeding incident which finally put paid to the marriage.
K-Fed confided to her: "I'd see her walking around the house guzzling vodka and Coke and looking very tipsy.
"Then a few moments later, I saw her pick up Jayden and start breast-feeding him. That sent me up the wall. I yelled at her, 'If you really wanna drink then make sure the baby gets bottled milk, not yours.'
"I was terrified she was poisoning my son. But she wouldn't listen. She never would. She treated me like one of her employees who bowed to her every whim.
"She screamed back, 'You can't talk to me that way!' But I had to stand up for my children as well as myself.
"Two weeks later she filed for divorce. I only found out when I heard it as a news item on the radio. I felt she was just trying to teach me a lesson for telling her off about the breast-feeding incident. But when I called she kicked off another row and screamed, 'You're nothing without me'. I never
wanted a divorce but now I knew there was no option."
Federline, 29, went on: "During the last few months I'd started picking her up on her parenting skills. She'd leave the kids near the pool unsupervised or drive around without belting them in. She always insisted what she was doing was right. There was no getting through to her. I still love her as she is mother to my two sons but I will never ever get back together with her."
Nicole said: "Kevin is battling for his kids as he genuinely fears they are at risk.
"He never shouts and screams about Britney in front of me. He does speak openly about his concerns for his children though." According to Nicole, Kevin is especially worried about the damage Britney's lifestyle is doing to their sons.
She reveals: "I was with Kevin on Monday morning when his kids turned up after spending time with Britney. He was overjoyed to see them, but deeply concerned about what they'd been through.
"On Monday he was treating Jayden for pink eye (conjunctivitis), and was worried Britney was to blame. He told me if they had joint custody he'd need two days just to get the children settled down and calm again after their stint away with Britney. He says she keeps them up and has no fixed routine which makes them over-stressed, over-tired and desperate for attention.
"He has tried to get Britney to change her ways, but gets nowhere. He gets so upset when the kids are with her that he won't switch on the TV as he knows there will be news footage of her with them in LA.
"He can't bear to see them looking stressed, traumatised and disorientated as she carts them off on another jaunt around town, seemingly for no reason.
"That's one of the key reasons why he went for custody in court."
The custody battle began in Los Angeles in September, the month Kevin met Nicole. He landed the first blow when his lawyers presented the LA Superior Court with a dossier about Britney's antics, including alleged lesbian flings, drug abuse, drinking and bad parenting.
We can reveal Kevin included the lesbian allegations after Nicole told him about her flirty encounter with Britney last December. Nicole, who met Kevin at a fashion party at Hollywood club Vice, said: "I told him Britney had once tried to kiss me. We met in the toilets of Beverly Hills restaurant Mr Chows.
"I was doing my make-up and I could feel someone staring at me. It was Britney, in a green dress and looking a bit spaced-out. She looked at me in a provocative way. I found it unnerving, but I smiled to be friendly.
"She then cosied alongside me by the mirror and asked to borrow my lip-gloss.
"I agreed, put some on my finger and let her rub it on. She rolled her eyes and giggled before suggestively rubbing it over her lips. It became clear she was flirting.
"She then asked for some more and kind of leant into me and glared intensely. I thought she was hoping to get me closer to her. When I told Kevin he nodded and said, 'Knowing her, she probably was'.
"I was shocked that she'd try to pick up someone in a toilet. I presume she's bisexual. I threw away the lip-gloss after that, thinking how tacky her behaviour was." Nicole revealed doting dad Kevin has created a real family home for his children.
She said: "Kevin has made a point of surrounding himself with genuine and pleasant people. Unlike Britney's place, his seven-bedroom mansion is a real home for him and his children.
"He has a housekeeper, cleaner and string of staff in all the time. The nanny comes in when needed and it makes for a real family environment.
"When you walk in you go into a hallway and there are pictures of him with his kids everywhere. There are the kids' toys stacked up including Sean's plastic truck which he rides around in the house. Jayden has his little cuddly toys in boxes as well. In the backyard the kids have a huge jungle gym activity kit, which they play with."
Nicole revealed Kevin has bedrooms not only for Sean and Jayden but also for his kids by former partner Shar Jackson-Kori, five, and three-year-old Kaleb.
She said: "Each of the lads has a bed in the shape of a Ferrari. The walls are painted with animals and shapes and are full up with toys. Sean's room has a big toy train set around the outside. Jayden still has trouble sleeping, so Kevin has put an extra Ferrari bed in his own bedroom."
Nicole slammed claims that Kevin is a wild-partying gold-digger.
The former Playboy Playmate said: "He may have been a party animal in the past, but I haven't seen him talk about or take drugs. He does like a bourbon and Coke, but he'll have a couple of those and call it a night.
"He has his home and that's where he spends most of his time now."
This weekend, Britney and Kevin were each spending one day with their children.
On Friday, after a three-hour hearing attended by the couple, Superior Court Commissioner Scott Gordon postponed a decision on Britney's application to win back custody of the boys. At one point a clearly disturbed Britney ran out of the court yelling: "Eat it, lick it, snort it, f*** it."
Nicole said: "I feel sorry for Britney. She has lost the love of a very caring, passionate and intelligent man.
"At the moment his priority is fighting for his children."