What legal boundaries can I set with my Ex?

My Ex and I are recently divorced. He plays a lot of emotional games with me. He will tell me one thing on the phone and the deny it in text and pretty much attack or berate me and make it out that I am delusional. We usually have a decent relationship until something like this happens. Then he starts threatening he is gonna take me back to court and take away my custody and all kinds of stuff. He pulled this with me, and I set a boundary where he is no longer involved in the decisions I make regarding the kids unless it has to do with what is in our court documents and outlined by the current state, we are in. He then said I was attacking him and all kinds of things. It is common behavior that is really hard to prove because in person it's like a switch and he is the most kind and respectful person to others. Anyways...What do I do? Do I get a lawyer? How do I afford one every time? I am out of job and in school and have kids full time...can he take them because of that?