Hi odearyme. What you're feeling: "All the things that happened 4/5/6 years ago are upsetting me now whereas at the time i just powered through." and you mention feeling that you've got PTS and are "angry and resentful of the unfairness of it all" ? all this is perfectly normal when you leave an abusive relationship. When you're in one, your standards of behaviour change and you accept things as normal that you would probably condemn if you were looking at someone else's relationship. It is only once you are out of the relationship that you start seeing things as they really were. That's when memories start flooding back and overwhelming you. The first stage in healing is to acknowledge everything that's happened to you. It's hard, I know, but a necessary part of moving on. THe reason it tends to cripple you is because it makes you realise how vulnerable how you were and still are, and it also rocks your self-confidence because you start questioning your own abilities, particularly your ability to read others. THIS IS ALL NORMAL AND IT DOES PASS! (sorry to shout, but while you go through this stage, which can last a couple of years sometimes, it is vital to keep telling yourself that you won't feel like this forever).
I was where you are now. Today, I have no feelings of bitterness or resentment towards my ex. Shortly after we broke up, however, was a very different story. It felt so unfair that he was able to come and go as he pleased, with no responsibilities, telling everyone his side of the story and 'blackening my name' while I was left homeless, with two babies, and unable to go anywhere to set the record straight.
I had the last laugh. People like my ex, and yours, can't help who they are and they eventually hang themselves with their own rope. Given time, he will probably screw up his current relationship (and if it lasts, she will be desperately unhappy within it even if she wouldn't admit that to anyone). Even close friends of my ex have started to see contradictions within his behaviour with no help from me! Those that remain blind to them are not the sort of people I would want as friends anyway, as they are lacking in insight and often have questionable morals. Abusive people are good at picking up partners and friends who will accept their behaviour, or at least accept their justifications for the behaviour.
I got through this angry stage by talking and talking and talking to my friends (bless them), walking my dog lots to stomp off anger, and reading everything I could lay my hands on about abusive and controlling relationships (it is important to realise that abusive relationships become abusive long before the first punch). Although it is not your fault your ex is a shit, it is important to understand your own role in the relationship so that you can heal, move on, and prevent yourself from repeating old battles with your ex now you are no longer together. I'd recommend reading "Why Does He Do That? Inside The Minds of Angry and Controlling Men" by Lundy Bancroft.
If your ex was dead, you'd have to make alternative childcare arrangements. I'm not wishing him dead, but you need to start thinking of him in that light in terms of anything to do with him helping you out in any way. It will always come at a price, so you need to remove that from the equation. This doesn't mean he can't have a good relationship with your DC; it just means it's all about the children.
With my ex, I explained clearly what I expected of him and that nothing else would be tolerated. If he became abusive I ended the conversation/made him leave, etc. It took about 4 months of this before he realised I meant business. Since then, however, we've never looked back. Today, we can actually share a coffee and a joke once the kids have gone to bed after he's been to visit them. I still don't rely on him for anything, although I always invite him to health appointments/nursery school reviews etc (and he usually comes along, but he knows I don't need him there), but he it's great that we can project a happy atmosphere around our children.
Good luck. Just remember, don't deny this phase. Work through it and you will be a stronger, happier person because of it. It will pass. Good luck.