Beebers your partner said he'd gone to Newcastle (is it?) and you found it he wasn't there but in Eastern Europe, did you say?
Why is it mental to challenge him on his lying? He told you he was leaving you as he didn't love you and needed some head space and then promptly moved into a flat. However it seems very strange to be lying to you about where he went to, if he has nothing to hide. Therefore you will have a lot of feelings of paranoia coming to the surface right now and it will make you angry when he lies about where he went, when there is no need to. And now he's saying you're lying? How did you find out he's not in Newcastle? I know you've got several children and are busy but it would help to have a bit more information so we can support you and advise you here, on why he'd claim you're now lying?
I think he maybe having an affair and hiding it from you, so he doesn't look so bad and there may also be some gaslighting going on quite frankly.
The truth is for you to move on you need some closure, perhaps you need to look for some evidence as whenwillifeelnormal often suggests. It would sure help you if you could get more to the bottom of his behaviour.
You also have the worry of your oldest child's father right now and what you think he thinks about the situation. You're in a very painful place with no explanation really that makes any sense to why he left.
When my H and I separated in October I had nothing but a web of lies and everything was so murky. It was awful and some days I shouted at the kids too much, they lived off fish fingers, chips, pizza and pasta. I subsisted on coffee and biscuits mainly in the early days. And immersed myself in mumsnet and facebook to occupy myself. I didn't feel like taking care of the my flat at all. I spent months trying to win him back, trying to work out what was truth or lies, I forced out of him the affair and then eventually that it had never ended and he was like a worm on a hook the whole time, not being honest and not being where he claimed he was. It's a horrible place to be. This is why I suggest you look harder into finding evidence. Better to have a clear picture now of what is going on than to continue to feel like you do right now.
Starting, the other girls put it much better than I could. It's not your fault. He chose to cock his life up and his family life through his actions. I know it was difficult last Christmas and still is if you see BIL isn't it? But try not take any responsibility for him in your mind x