You are suffering the effects of Parental Alienation, yes, that's a thing. My husband is also a victim, or more accurately his children are. As you are experiencing, mom is bad mouthing dad at every opportunity to anyone who will listen, including her children, and has managed to completely alienate her daughter from dad. Very painful, and completely unnecessary as all she has to say is either her narrow perspective and opinion or plain lies. We have been told that the kids will figure it out, that he needs to just love them and not bad mouth mom back. So that's what he is doing. The boy is 10, the girl is 13, we expect to have a number of very difficult years. We have to believe those who went before us that it will get better and that the kids figure it out. You are fortunate in that you have the opportunity to live life with your son well away from mom's everyday interactions. It also sounds like, though young, your son has the measure of her. Keep doing what you are doing and don't drag your son into it, just love him well.