Hi sid,
I'm sorry you're going through this -- the affair had to be painful, and then to learn that your wife has BPD as well. It's tough. How are you holding up? It's good that you're seeing a therapist.
I wonder if this might be helpful:
PERSPECTIVES: Is it better for the kids if I stay or leave?There have been studies that show that kids who grow up in divorced homes have more problems in life than kids whose parents stay together. Would having a BPD/NPD parent (or other abusive parent) change this outlook? If you leave, do you think your kids have been harmed by the friction between you and the ex? Would things be better for your kids living in a two-parent home situation? If you are the father, do you believe that leaving your marriage means leaving your kids?What kind of relationship does your 18-year-old have with you? Would he or she want to live with you or with your wife?
Hang in there. It's tough, many of us have been in your shoes and are here for you.
You're not alone.
LnL