|It takes a great deal of strength to be in a BP relationship and not be emotionally injured by it. As you cannot escape the natural human impulses to "recoil when raged" upon or "be overly protective" when idealized, it really important to have other outlets / escapes to keep yourself grounded
Strength: It takes a great deal of strength to be in a BP relationship and not be emotionally injured by it. A person in a weak emotional state, who feels wounded/abused, or depressed is likely to be consumed by the relationship, confused by the intense rages and idealization, and finding their self worth in decline. If you chose this path, you've got to be very strong and very balanced.
Realistic Expectations: A person with BPD is emotionally underdeveloped and does not have "adult" emotional skills - especially in times of stress. If you are in this type of relationship it is important to have realistic expectations for what the relationship can be in terms of consistent respect, trust and support, honesty and accountability, and in terms of negotiation and fairness, or expectations of non-threatening behavior. It is important to accept the relationship behavior for what it is - not hope the person will permanently return to the idealization phase, not accept the external excuses for the bad behavior, and not hope that changing your behavior will improve things.
Accept the Role of "Emotional Caretaker": According to Kraft Goin MD (University of Southern California), "borderlines need a person who is a constant, continuing, empathic force in their lives; someone who can listen and handle being the target of intense rage and idealization while concurrently defining limits and boundaries with firmness and candor". To be in this type of relationship, you must accept the role as emotional caretaker - consistently staying above it.
~ Maintaining routine and structure
~ Setting and maintain boundaries
~ Being empathetic, building trust, even in difficult times
~ Dont tolerate abusive treatment, threats and ultimatums
~ In crisis, stay calm, dont get defensive, don't take it personally
~ Dont protect them from natural consequences of their actions - let them fail
~ Self-Destructive acts/threats require action
And at the same time, its important to understand that you and your behavior cannot rehabilitate anyone - you can only mitigate the situation. Rehabilitation requires an individual's deep personal commitment, consistently, and over time.
Protection: Difficult things will likely happen in a BP relationship and it is important that you try to protect everyone (you, the BPD, the children) - financially, emotionally, etc. Be prepared for digressions when they occur - they will. This could range from controlling the bank accounts, to educating the children, to having a suicide threat plan. You can mitigate some of the damage.
Preserve Your Emotional Health: The intensity of emotional reactions, and the rage take a toll on even the strongest. Since you cannot escape the natural human impulses to "recoil when raged" upon or "be overly protective" when idealized, it really important to have other outlets / escapes to keep yourself grounded. It's important not to become isolated. It's important to have a significant emotional support system for yourself (e.g., close friends) that goes beyond the relationship.
Understand Why: There are a many reasons to be in BP relationship or to try. It's a deeply personal decision. Sometimes the reasons are unhealthy- such as BPD/NPD relationships, BPD/Co-dependent relationship, etc. It's important to understand your own emotional health and what motivates you to "stay in" and build a life that "evolves around" and has to "continually compensate for" the acts of a destructive person. Many professionals enter therapy when they are treating BPD to stay grounded. It is a good idea for you too.