Having an ex try to continue to manipulate your emotions is not fun at all, when all you really want is for them to leave you alone and give you some space so you can finally start to get them out of your head and move forward.
I agree with the others that you should do the mediation...as you are eligible to legal aid, perhaps you could enquire with them about attending the legally assisted version...means you would have a lawyer present. I also agree you need to take some of the control back...
I know you are emotionally exhausted right now so your motivation is waning but walking away in the hopes he will just leave you alone is not a fool proof solution. You have kids together that keep you connected and there is no guarantee that the treats of court or dv (or even him manipulating you by continuing to say he loves you. When he has re-partnered etc.) will stop or things will get easier.
From what you say here...he may need a good reality check...if mediation fails again, Court may well be the place to assist him with that. In other words, he won’t be reasonable and continues to threaten you with court. You take his sorry ass to court instead...no more threats of court (and you have taken control)...will also mitigate some of the dv threats as it won’t look too good for him if he continues along those lines when the behaviour can be raised before the judge. Apply in relation to children and property...
For now...stick to communications only in relation to the children, unless its an emergency, if you need to tell him something about the kids text it. If you answer a call from him and he strays from discussing the kids...politely tell him you need to go and hang up. Do your 14 year olds have mobiles?...if so, they can contact him directly?
Is the 2 year old spending time with dad?...are you by any chance supervising these visits? If info revolves around the kids there should be no reason, at this time, to correspond with his new partner...how do you know that her contact with you to discuss your ex is not a set up and being recorded?...entrapment springs to mind.
As I said, I agree your best option for now is to do the mediation and go from there. I wish you well.