Hi there snickers!
I have no legal advice, just wanted to send you some huge cyber hugs!!! Your stbx sure is a pea brain idiot!! What nerve to ask YOUR PARENTS if he can bring a woman with him to stay with them!!! What a pea brain idiot!
Did you go thru the courts for what he is supposed to be paying you? If not, I would. From here on out, I definitely would be looking out to financially benefit myself - your kids come first. And it's sad that their Father is not thinking of them first. He is thinking of himself first. Also, the little amounts - here and there you said he gave you for help - keep track of all of that. Document everything.