Okay, thank you for the information. She does sound like there are definitely traits of bpd, though I cannot say with any certainty, unless I would diagnose through an in person assessment. I'm sure you are concerned about how her behavior is affecting your son and that is your first priority. He will not understand this and will more likely internalize her behaviors if she starts blaming him, etc. Not to mention her rages are certainly going to be very frightening for him. Therapy once every 2 weeks is not enough. You could contact her therapist and let him/her know about the threats and the rages, that it's happening in front of your young son, etc. That is the best thing to do here. If you do feel that she is in danger of harming herself you can call 911 or take her to the emergency room, and also call the therapist. With someone, who is bpd, there do need to be consequences to the behavior. You can't control or reason with the person but can set boundaries. When you blame my son, I will... leave the house with him, not allow you to be around him, go away for the weekend with him for a break, etc.
Things you will do in response to her behavior. kind of dealing with a child. Also, there is a book called Stop Walking on Eggshells, What to do when someone who care about has BPD, by Rande Gerber. You can get it an amazon.com.
I would also look into some counseling for your son as well, so he can feel heard and voice anything that is bothering him. Be sure to tell him yourself, that none of this is about him at all, and that she is mentally ill, and you are taking care of the situation. Also, if the behaviors continue and don't improve, you will have to decide if you can continue to have your son around this behavior. Meaning, he needs to have a safe and secure home environment and that comes first here. Do not hesitate to contact her therapist, in fact do so today and let the therapist know what is going on. There is good treatment for borderline disorder called DBT, which helps them to regulate their emotions, reduce the rage etc. Here is a link about this therapy. You could ask the therapist is they know about this therapy as it's proven to be effective.
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