Best ways to parallel parent?

Any tips on how to parallel parent with a high conflict person? My daughter’s dad is just impossible to work with. Against me 24/7, talks down to me all of the time, ruins big occasions (birthdays/christmas) it’s his way or no way in every situation. Makes demands and changes plans all the time. I honestly feel at breaking point. My anxiety is at an all time high. I just don’t know how to move forward with this. There’s no court order in place, I’m terrified he will get more contact so I’m trying my absolute hardest to keep that from happening.