BW here, and I have a child with BPD and alcohol/drug addiction issues. We've had other WS here with BPD and bc of my child, I sense it can add some layers to the infidelity dynamic.
First, I agree that what sounds to me like panic-driven desire to R may not only NOT accomplish what you want, but can work to stall your own journey to heal and grow and change the behaviors. IOW, trying to R cannot be the sole focus of your work.
Are you in IC? Does that IC include DBT?
If there is trauma in your history, have you worked to address and heal that?
I also agree with others that the lying must stop IMMEDIATELY. Write out a complete and thorough timeline of your infidelities. Many suggest (and I agree) to do one that is a "PG" rated version and another with the gory sexual details. I would try and work with an IC in doing this, as I suspect it will trigger a TON of shame (and that may be exacerbated for you bc of the BPD Dx).
And then rip off the damn bandaid - preferably in collaboration with your MC and, if your BS has one, his IC.
Also, 12 APs in 2 years screams of SA (sex addiction), which is it's own kind of special ball of wax (and no surprise when there is alcohol addiction already present). I am a fan of CSATs (certified sex addiction therapists), tho they can be hard to find and often don't take insurance. Like any IC/MC, all CSATs are not alike, and the current "preferred" modality is the relational betrayal trauma model.
I'll also echo the questions about what books you may have read, and add podcasts to that mix. There are several pretty good podcasts about sex addiction, tho the ones I like are geared toward the BS more than the WS. I am a big fan of Helping Couples Heal and you may find some of their info useful. There's another called something like the betrayed the addict and the therapist (that has a LOT of episodes, but I found it to have a lot of sides, but not so focused on the meat & potatoes, if you get the drift).
You will likely need to do some solid learning about shame and trauma. IMO, Brene Brown is the queen of shame and she has several books that may be helpful. My personal favorite is a 6-8hr audio I got free from my library via Hoopla called "The Power of Vulnerability" that is the audio of a series of lectures (and it has more than you'll find in her stuff on youtube).
As to trauma, The Body Keeps the Score by Bassel Van der Kolk is kind of my trauma bible. Nothing to do with infidelity (or if it does, it's ancillary and anecdotal). I wouldn't be surprised if you have trauma in your history, and that book can help you understand the ways in which trauma impacts us - and also your BS. That trauma is not an "excuse" for your decision to cheat, but it may help guide you in healing from the past hurts as well as finding ways to be supportive of the trauma your BS is likely experiencing.
My WH's CSAT recommend a workbook on empathy (something many SA really need) called Help.Her.Heal. by Carol J Sheets. It's relatively new and wasn't available via my library. It is specifically aimed at sex addicts and how to find ways to "fake it til you make it" on the empathy front. Maybe more for the "back burner", but didn't want to forget it.
In my experience, the DBT piece is really the first - and crucial - step in addressing this crap, as the focus is to find ways for someone with a BPD Dx to learn to manage the flood of emotions (that are usually the precursor to some really bad decisions).
Godspeed
ETA: Sissoon and I cross-posted, but this is REALLY important:
Accept that what you tell him may cause him to choose D, but know that continued lying will (probably) cause him to D.
[This message edited by gmc94 at 12:28 PM, April 20th, 2021 (Tuesday)]