I agree with everyone else (including MoGaga, it was really hard to read, so you might get more replies if you do use paragraphs in future).
He isn't your priority, your children are.
He is dangerous, not just when she is around, but the rest of the time too.
Harvest Festival is neither here nor there, really. Your children aren't safe with this man, so he should only be seeing them supervised by a responsible adult, whether that be you, a relative or a professional. He certainly shouldn't have them over night or in the car.
The children might not like that, and might blame you for that, but their safety is paramount.
This man really doesn't need your sympathy, but your help, I'm sure, he is grateful for.
Keep his probation officer and social services in the loop, that is absolutely the right thing to do.
How old are the children? Do they know the whole story?
I hope this sorts itself out, you sound like you could do with a rest from this selfish man. :)