My ex moved out in Jan (my choice) We were managing to get along ok until he borrowed my laptop in March, I got it back & found he had been on a dating website, had a new girlfriend & had also been on the dating website since 2008 when we had DS 
I told him I didn't want the kids to meet the new girlfriend, but a couple of weeks back, DS (4 yo) came home & said he'd met Daddy's cousin called x - I know he doesn't have a cousin called x. I was furious with my ex & told him, so now he refuses to speak to me/ text me & has now said I must only contact him by email.
He now he wants to change the arrangements with the children. Previously it was him to babysit every Mon & alternate Fridays, with alternate Sat/Sun staying at his Mum's house with the kids. Now he said things have changed & he doesn't want to come round Mon or Fri.
I don't want him to have the kids at the weekend as I know he'll ber seeing his girlfriend with them & I don't want to confuse my DS particularly as it is very early days for him & he obviosuly still wants us to get back together. I know my ex is being pig-headed but I wish he could see how hard he is making it for the kids by not seeing them very often :(