Trying something different.

Putting myself in stbx's shoes:

"I have started a relationship with someone else. I am out doing my shopping on Sat morning when I bump into my kids in the supermarket.

They go pale and look upset. I panic and don't know what to do. I feel like dying.
I am scared my ex H is going to make a huge scene - scream and shout and rant at me and punch my new partner.

I walk around for a while not knowing where i am or what I'm doing.
My new partner calms me down and tells me to just go up and talk to my kids calmly and nicely. Reassure them that everything is Ok. I am their mum after all.
Perhaps this is a good time to introduce them to my new man?

I go up to them.
My kids tell me to F off. My ex H tells me to leave them alone. I am horrified. They have no right to speak to me like that. I am the mother.

I try again but get the same response. Everyone in the shop is looking at me. I am humiliated and embarrassed.

This is not my fault. I am just doing a bit of shopping with my new partner. Why is my ex H being such a bast--rd?
He has turned the kids against me.

I stew for days. My D is rude and screams at me when I call her on the phone. I have to teach her to behave properly if my ex H will not. I will withhold something she really wants (her phone). My S refuses to go anywhere with me. He has been tricked by his father into thinking I am bad.

I have to insist that my ex H allocates time for me to see the children on a regular basis. My new partner tells me that this is standard practice. My ex H is obviously manipulating them and me, and is withholding them from me in order to punish me.

I love and miss them so much I can't bear it. They are turning into horrible children and I need to be more involved in their parenting.

If only my crazy ex H would do the right thing... I've got this all worked out - it could be so simple.

But he is one of those unable-to-let-go maniacs. My new partner can see it - he calls him a bunny boiler. My ex H will ruin everything for everybody. This is not turning out like it should and it's all because of that crazy loon. "

Question is, How to move forward from that way of thinking?