No contact is difficult of course when there are children involved. You can set agreed upon visitation, arrange safe forms of contact, but in the end, any connection to you is an opportunity for an alcoholic to infect you with whatever is eating its way out of them. Sometimes it's regret, sometimes anger, sometimes fear. They have vomited it on you to relieve themselves of it for so long that it is a reflex when that connection is made to you. Like a gag reflex to a foul odor.
I don't have kids with my XABF, but we had the pets in common. He would call under the premise of seeing the pets, but he couldn't even leave a voicemail about seeing them without venting some agitation or venom my way. A 60 second voice mail, and he couldn't hold back. I stopped answering then I blocked his number. If he can't handle 60 seconds talking to a recording, how can he be civil in person for any length of time.
Do what you can to cut off that connection. Cut the ringer off at night. Send his calls to voice mail. Refuse phone contact and insist on text, and put a limit on it with your phone company. There are things you can do to make this better for you.
Alice