communicating with ex husband.

Hi there. I am struggling with my ex husband . He communicates what he wants – when he wants and then ignores the rest. The most recent example of this just happened over Christmas break. My ex was taking our children for 5.5 weeks (another whole story of manipulation) and leading up to the trip was asking me to do him tons of favors. Every day he was asking me to order them different things and telling me what and how and when to pack etc. I would always immediately respond and comply.. even though he could have ordered them flip flops and hats and all the things he was demanding I do for him. In my responses I would occasionally ask when I could expect the child support check. He would never answer. He would respond with another demand but no information around the check. In the final days before leaving he started demanding I drop the bags off at his house and I said I would swap the bags for the check. He still ignored me. Then he started asking the kids to tell me to bring the bags to him. I said not to worry, the bags are packed and ready and dad and I are just dealing with a few loose ends. Cut to the night before they are leaving – at 9:30 pm when I am in pajamas he says bring the bags I have your check… So I went over and brought the bags. He threw my check in the snow in front of my kids and yelled at me for holding the bags saying I was crazy. When I got home and looked at the check – it was fake. Now they are all back from vacation and my son fell terribly behind in virtual school. I have now been dealing with the teachers and doing everything I can to help my son catch up and raise his grades. I asked my ex to please help support me and our son in his academic career. He has a history of taking the kids out of school for no reason – just to hang out and he never seems to make them do homework etc on his time. He said would but we need to communicate better. I was like… whaaaat???? He does this constantly. He does horribly mean things then afterwards says we need to look forward. I get that we need to look forward but I have whiplash. He does completely insane things (way more insane than a fake check) and then afterwards conveniently asks that I look forward not back… I am exhausted. I catch him in lie after lie and I sadly just don’t trust him or believe anything he says. Help!!! Thank you:)