I feel for you. It sounds like your ex is excluding from parenting decisions and that can be very hurtful. I’ve been there as well.
In my case the children ended up resenting their mother and as they got old enough they have moved in with me. The main source of conflict I have with them now is when I tell them they should contact her as, despite her behaviour, she is still their mother. I’m not saying your ex is doing that but if you show them that you love them and put their needs and happiness first they will come to see that in the medium term.