Hi TrueGrenadine,
Getting yourself to a strong place is job number one. It takes a lot of strength to not be emotionally injured in a BPD relationship, and if damage has been done, it's important to get yourself centered.
Have you tried validation with her?
This and other communication skills can help minimize the cycle of conflict. It takes some practice to get it right, and to learn how to stay grounded when a BPD loved one is in an emotional dysregulation.
Core challenges with BPD include impulsivity, intense shame & self-loathing, and extreme rejection sensitivity. There is often a tremendous amount of anxiety over things that tend to roll right off of us. You may need to change how you prepare her for transitions, and how you talk to her when she is winding up. Validation means accepting and acknowledging her feelings, even if you don't agree with what she is saying. Not easy! It can also be the difference between conflict or not conflict.
It also helps to sort out what your values are so you can build boundaries from there. Until being in a BPD relationship, it had never occurred to me what my values were. This helps us stay grounded in who we are and what is important to us. Without being clear about values, it's easy to have boundaries eroded. People with BPD have an unstable sense of self. And that can look and feel a lot like boundary busting, anything to manage the feeling that things are out of control, and the intense shame that goes with it. Being the emotional leader in the relationship will fall to you.
For example, your value may be based on having a sober partner. Your boundary may be that if she uses again, you will protect yourself and your kids. The rule might be that she can only live with you if she is sober. The consequence is that she needs to move out if she is found using.
Another value may be around civil conversations. Your boundary may be that you will protect yourself and your kids if there is a raging, abusive conversation. You may enforce that boundary by choosing to walk away, or hang up, or leave the house if/when there is an explosive rage. The rule may be that if she damages anything during a rage, she pays for it with her own money.
There are many other examples, and there is no one value or set of values that are right or wrong, they're different for everyone. In general, though, it can be helpful to have the conversation when she is not dysregulated so that she understands where the boundary is, and the consequences. And be prepared that she will test those boundaries to see if they really are boundaries. You have to commit to being consistent, even if it's uncomfortable or inconvenient for you.
Lots to learn! I hope you'll let us know how you're doing.
LnL