Hi Tocyo,
I'd like to join RolandofEld in welcoming you.

I"m sorry that you've been going through such a hard time in your marriage but also congratulations on 3 years sober! I was an addict when I was in my young 20s and I know how hard it can be to not turn to self-medication during times of stress.
I think it's great that you are working your steps but given the aspect of BPD, is it possible to revise your steps a little. When it comes to my own boundaries I often refer to this quote: "If it is possible, as far as it depends on you, live at peace with everyone." THe "if it is possible" part is important because sometimes it's not possible, especially when it comes to someone with BPD. Admitting your wrongs is important, but if they are being used as ammo later, can you admit them to yourself, to another friend, etc. instead of to your wife?
Have you ever looked at the steps in Al-anon? They are geared more towards the family of loved ones with alcoholism, but from what I understand they also look a lot at co-dependent behavior, which is what living with someone with BPD can do to us.