Welcome! Is your son still a minor or is he already 18 as a Sr in High school? If he is still 17 you will have more power to step in .
Good for him that he recognized he had to go to ER and he is signed up for IOP. You have a good plan in place. Here from our forum is some reading for you to peruse:https://bpdfamily.com/content/setting-boundaries.
Please remember what may work for some may not work for others, lots of trial and error is involved. Patience and lowered expectations on your part is key. Look at what is important to you and can you live with any consequences you set up for him if he crosses the boundary?
Now for your own care- joining here is a good first step . Take a look around here, peruse the drop down menus up top. You can also click onto anyone's name here to read their previous posts/ get backstory. You are not alone.
~I would suggest familiarizing yourself with BPD here are some suggested readings:
Stop Walking on Eggshells: Taking Your Life Back When Someone You Care About Has Borderline Personality Disorder by Paul T. T. Mason MS, Randi Kreger
The Essential Family Guide to Borderline Personality Disorder: New Tools and Techniques to Stop Walking on Eggshells by Randi Kreger
Overcoming Borderline Personality Disorder: A Family Guide for Healing and Change by Valerie Porr, M.A.
We also have a Library with book suggestions and reviews.
Here is a link to it...
https://bpdfamily.com/message_board/index.php?board=33.0. It is important to build your own network and this forum can be a part of that. Some of us also have our own therapists as well . 12 Step family programs ( Codependents anonymous) are free and some are online. These help with detaching and to keep from getting lost in the child's BPD.
Please write back here as you are able.