After the final D & D

So, just to keep you updated...
I got my final D & D three months ago. (called me a slimy piece of sh*t and an adulteress - yes, we can all say 'projection')

So, Even though I had moved out two years ago with my three children, he had been able to hoover his way back into my life on 3 occasions by going to counselling and anger management (well, a fat lot of good that did! as if counselling can work on such a disordered person) But it was definitely all off once and for all three months ago when I laughed in his face.

Anyway, I want to thank everyone on this site for their heartfelt contributions, because without them, I think I would have been really upset by what has followed the D & D.

One week later he was off to Sydney (we live in Melbourne) with the kids for a 'holiday'. Dumped them with his parents while he pretended he was a teenager again. Obviously hooked up with a woman there. Next weekend, spent the weekend in Melbourne with a 'friend'. (no phone calls to children) Next weekend, back to Sydney (no phone call to children the entire weekend). AND the next weekend to Sydney (again, no phone calls).
THIS weekend, his parents came down for my son's birthday. My son and I have been discussing how I will buy him an x-box for Christmas.

I received a phone call yesterday from exNH saying that he found a second-hand one for cheap and that we should buy it. I said no, I would think about, but that my son and I would organise it ourselves.

Then I overhear my son on the phone to his friend saying that his dad was going to get him an x-box for his bday, but he can't get one cause his mum won't let him!

Then my exNH just went and bought him one TODAY. What an a88clown!!!
So everyone, what do I do? He's such a lowlife scum. I can't believe how he can ignore his children and pretend they don't exist while he's out shagging god knows who. And then when his parents visit, he puts on the whole SuperDad mask, it actually makes me feel physically sick. I had to get on this forum and get it out of my system because otherwise I think I could throw up.
What should I do?