Though I am no doctor nor psychologist, it's possible you have more than BPD in your case. It sounds like he likes to be attention seeking, the center of the drama? If so then it's possible he also has traits of
Histrionic Personality Disorder. People can have traits of more than one disorder, it is called 'co-morbid'.
One issue you're dealing with is that most courts appear to avoid naming a diagnostic label. (Well, except for murder cases.) Nor do they excel at detecting and resolving adequately the long term patterns of sabotaging obstruction. They don't try to fix people, they deal with them as they are. Obviously, when the root causes of a person's behavior are virtually ignored, the solutions sought often are insufficient for long term resolution.
Regarding Parental Alienation (PA), the psychiatric community resisted Richard Gardner's approach to PA attempts. Despite the facts of the behaviors, it didn't fit well with their models. That's why it also didn't get much traction in courts and remained disputed for so long.
Dr. Craig Childress has come out with a new approach that does fit the psychiatric models, that
PA is an aspect of child abuse. This approach seems to be gaining traction. Please take a deep look into his videos, blogs and writings.
May I ask the credentials of the Guardian ad Litem? (Around here we often use the initials GAL.) In some areas the GAL can be a newer lawyer willing to take the lower pay of such a case. The GAL may not even have extensive training and education on custody and parenting issues and the impacting parental behaviors. What I'm saying is a GAL is not automatically an expert. You may need to seek out an expert on such matters.
The GAL assigned to my son was a social services lawyer for children. But when I did research (okay, internet searches) what I saw was that she authored articles about children in juvenile court, that is, kids who got into trouble. So I was a little concerned about her being able to deal with my oppositional ex. In her first case with us, I sought custody and majority time, she agreed I should have custody but wanted ex to keep her equal time so she could get child support and hence behave better. Well, surprise, surprise, ex didn't behave better. Duh. The second case in court she came around to reality and recommended I get majority time. It delayed fixing things for our child, by then a pre-teen, by almost another 3 years.
