Federline raised this concern to his girlfriend Nicole Narian, contactmusic.com reports. Speaking to a newspaper, she said Federline was scared that Spears frequently breastfed her younger son while drunk and it may harm him.
He reportedly told Narian: "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."
He allegedly added: "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."