My name is XXXXX XXXXX I'd be happy to answer your questions today.
If there is a court order giving you reasonable visitation, and he doesn't honor that, you can go back and have him held in Contempt of Court. Your ex-husband isn't allowed to ignore the order just because he's upset with you.
Second, you can go back to the family court
and request a modification of the custody order any time there is a material change in circumstances. If the two of you were living together, and you're moving out, that should qualify. Then, you would just have to explain to the judge why it's in the best interests of the child for you to share custody. There's a presumption in the law that children benefit from having a relationship with both parents, so unless there's a good reason that you shouldn't be allowed to spend time with them, the request will likely be granted. You may not get 50-50, depending on things like proximity and school, but you can try to get a set schedule so you're guaranteed to see the children at specified times.
I wasn't able to find the forms online, but you may want to call the clerk of the court to see if they have any. Otherwise, you can see if you qualify for legal aid, or visit a law library to look at books that will show you how to do it.