I have a question my boyfriend son is 5 years old and we have a feeling that the child's mother is brainwashing the child against him. There has been 10 months of supervised visits with him and his son at the courts and there was never a problem with any visits and always went well. Now the child does not want to come with my boyfriend, as his mother is telling him that he has another mother for him. She is always saying negative remarks to my bf's son about him and now he is afraid of my boyfriend. What can we do to have this stopped? Please help

There is nothing you can do to stop her from her remarks. You can try and talk to her but most parents that do that need counseling to make them see how bad that is and to stop.
The only thing you can really do is reassure the boy that "daddy is a good daddy and loves you and don't let anybody confuse you that he isn't."