I think you should consider marriage guidance.
Relate is all about relationships and helping you make changes for the better. If you want to talk about your relationships past, present or future, how your family is affected by your relationship, how you can improve your relationship, how you can manage a separation constructively, how you can get over a break up, Relate is there to help.
You BOTH need help.
She has displayed this by her actions -threatened suicide etc
It may well be that she "knows" the relationship is failing and needs more than ever the support needed to get through the difficulties that separation brings.
It is naturally human for us all to consider "ourselves" in all this but she is the mother of your children and it is in their best interests that they have a meaningful relationship with BOTH parents.
It is a good thing that you assist her to have some time off from the pressures of home with some "palliative care".
"I have tried talking too her, threatened to cut off all access and go thru courts nothing works ... she either responds with more abuse or threatens to do something stupid........"
This reveals a worrying aspect.....remember contact (access) is the right of the children not something that either parent should use as a weapon to control the other. That most likely has been percieved as a "threat" and with respect adds to the cycle of percieved abuse.
We have to break the cycle and address the fundamental problems which beset your family otherwise the family will implode and that will cause untold dmage to your children and you both.
No doubt when the latest developments come out your wife will feel even worse and a greater sense of abandonment...what you have to do is make sure this doesn't happen.
It will call for a great deal of honesty and this will be a real test of your new girlfriend's committment to your relationship. She will have to be very understanding as it is vital if your children are to be protected that your wife is given support for a considerable time to get over the marriage breakdown.
I think if the marriage guidance is attempted it can be explained that it would help to bring the marriage to an end but that does not mean your committment as a father comes to an end.
"Parental responsibility" is what you both have in relation to the children -there are times when both parents will have to prove and show that.
The secret here is to find what you and your wife have in common which of course are the wonderful legacy the marriage will leave namely the children.
Concentrating on the children will help to mask the other issues and hurt. They can't be ignored though.
Now one can immagine that if you are going to put in all this time to the children and indirectly helping your wife then your new girlfriend may feel "left out".
If you have a young daughter I imagine she will be over the moon to have a sister ultimately-
Keeping all this hidden from your wife will not help -I think you have to get professional help from Relate to help all the family to "deal" with these issues. At the end of the day if your wife is reassured that you are not trying to take the children away from her and this is made clear from the outset then from little acorns large trees arise.
I do hope things get better -the first step is to contact Relate and take it from there.