I am not representing my views and/or opinions as anything more than personal experience based upon over 15 years of experience with a BPD individual and having produced one (of two) children diagnosed with BPD. I am not a physician, therapist, counselor, attorney, or any other professional. Take any of this information that you may find helpful and leave the rest.
BPD is one of the most difficult disorders to diagnose and treat. Unless the BPD individual is thoroughly courageous, honest, and willing to do the grueling personal work, he/she will continue a downward spiral. There is no cure for BPD and medications (i.e. antidepressants) tend to mask the unnerving symptoms of this ruinous disorder, rather than "curing" the symptoms. As with most psychological/psychiatric conditions, this disorder can be successfully managed. What is imperative for the friends, family, and significant others of BPD individuals to understand is that they are NOT crazy!
Many of the traits that non-BPD find attractive in a BPD individual are traits that are non-existant. The outward appearance of the BPD person may seem to be caring, loving, passionate, concerned, etc. - these "traits" have been carefully cultivated in an effort to hide the BPD individual's personal insecurities, emotional trauma, etc. Once the non-BPD has been ensnared (for lack of a better description), they are typically separated from their own network of support, down to close family members. A noticable orgy of lavish spending can be documented as the BPD individual cycles through highs and lows, as well as rabid sexual behavior. Intimacy does not always refer to sexual activity, and the BPD individual is absolutely incapable of emotional intimacy. Sexual activity, in particular, replaces intimacy. In my case, my ex-spouse replaced extravagant spending with sexual foreplay and would often make enormous purchases without my knowledge - only years later, when we were forced into joint bankruptcy, did I learn of a number of "secret" loans and credit accounts that had been opened. The potential for emotional and physical violence and abuse is an almost certainty in a BPD relationship. Because the BPD individual cannot control him/herself and is incapable of admitting mistake, they will seek to control others and lay blame wherever they can, to include: spouses, friends, children, in-laws, teachers, co-workers, etc.
The BPD individual strives to present an acceptable outward appearance, so much so that the non-BPD individual will often appear unstable, even to their own family members. Or, the non-BPD individual has accepted the role of co-dependent to such a degree that "outsiders" will often view the BPD and non-BPD individuals as "...the perfect couple..." The BPD individual will often have a store of psychological knowledge as a result of the non-BPD indidual attending counseling or psycho-therapy and use specific buzzwords to further control the non-BPD individual. At this point, the non-BPD individual has fallen into the status of abuse victim. Often, the abuse victim ends up on psychotherapeudic drugs, but the spiral of abuse continues: emotional, verbal, physical, sexual, financial, spiritual - the non-BPD individual finds that they have become a shell of their pre-BPD-victim selves, and, regardless of years of counseling, see suicide as a viable alternative. Another symptom of co-dependency of the non-BPD individual might be frequent illnesses and/or injuries, feelings of helplessness (nothing that the non-BPD individual does is "up to par" or "acceptable" by the BPD individual), use/abuse of prescribed medications, doctor-shopping, to name a few. Another glaring indication is recognizing that "friends" are selected, screened, approved, and allowed by the BPD individual, as per his/her needs, at the time. Most non-BPD individuals have an extraordinarily difficult time cultivating a network of friends unless the BPD individual is actively involved in the process.
It is important to note that the non-BPD individual cannot, under any circumstances, be held responsible for the actions of the BPD individual, their diagnosis, or the success of their treatment. The non-BPD individual will often be torn between what they "love" about the BPD individual and those aspects that are intolerable. Often, the non-BPD individual will accept the abusive treatment of the BPD individual because they mistakenly believe that they can "help" their BPD individual "change," or "see the light," or "get help." The non-BPD individual IS NOT RESPONSIBLE FOR THE BEHAVIOR AND/OR CHOICES OF THE BPD INDIVIDUAL! The non-BPD individual may have agreed to be involved in a number of bad choices and/or decisions, but it is extremely important for the non-BPD individual to acknowledge their compliance and refuse to accept any/all stupid, dangerous, risky, foolish behavior and/or decisions at the behest of the BPD individual. In my case, I was counseled that I was no longer required to defend my personal choices, nor was I required to engage in arguments or bad behavior. Unfortunately, my BPD individual would follow me from room-to-room, screaming insults and ridiculous allegations at the back of my head. During this time, I began to recognize and accept my role as a co-dependent and put an end to my compliance in such choices as: financial coersion of my parents; fraudulent insurance claims ostensibly to "pay off bills;" religious/spiritual compliance (being "allowed" to practice one specific religion); sexual compliance (performing sexual acts to appease the BPD individual); inventing cover stories to excuse and/or dismiss unacceptable behavior; etc. Although the coping techniques opened a very positive door for me, emotionally, the BPD individual refused to acknowledge any of the behavior, choices, and coersions that had irreversibly damaged me, our children, and our marriage. Once it was an absolute certainty that the BPD individual wasn't willing to engage in honest, courageous, and intensive personal therapy, I made a choice to end the relationship, even at the expense of my extended family members. I escaped from the morass of BPD with my life under my own initiative and effort. Others are not as lucky.
Sadly, most people who make an effort to exit a BPD relationship find that they are virtually friendless (and, sometimes without support of their own family members), fearful, and in physical danger from their BPD individual. If there are children involved, they will be used by the BPD individual as tools of coersion, threat, control, etc. In some cases, the only way to survive a BPD relationship is to formulate a plan of escape, taking only the children, important documents, a few clothing items, and get to a "safe house," whether it is a shelter for the abused, distant relative, or agency dwelling.
Because most BPD individuals will not pursue therapy, counseling, or behavior management, exiting the relationship is often the only means to survive, mentally, physically, emotionally, spiritually, etc. Again, if children are involved, they are at extreme risk of watching the behavioral cycles, learning to mimic them, and possibly evolving into BPD individuals, themselves - there is strong evidence that BPD is genetic.
If you are involved in a BPD relationship and in fear of your life, contact your local police department, immediately. DO NOT THREATEN to call the Police! Do not ever threaten to do anything that you have no intention of following through on! Do not announce your intentions, ever. "I am calling the Police," is almost a guarantee that you will jeopardize your life. DO NOT keep any lists of counselors, attorneys, friends, etc., anywhere that the BPD individual could find them. DO NOT use a computer or cell phone that the BPD individual has access to as a means of communication, research, etc. - any and all outside relationships will be used against you! If you need to communicate with your safety network, use pay phones and calling cards, and public library computers. Do not, under any circumstance, tell the children of any plans that you may be formulating, such as: "You know, mommy hasn't been well, lately, and we might have to go on a little trip/vacation without her." BPD individuals are extraordinarily clever at wheedling information from children who are also victims of the BPD individual. DO NOT tell estranged family members of your plans - more than likely, the estrangement was due to the machinations of the BPD individual. DO NOT, ever, ever, ever, allow firearms or other weapons to be stored in your home - if you have a reasonable concern for your safety (or, for that of the BPD individual and children), remove all weapons from your living quarters!
Keep a running log of dates, times, topics, discussions, and bizarre/abusive behavior before, during, and after you exit. Record precise quotes and/or behavioral descriptions without embellishment or emotional discourse. Include your own remarks and behavior, even if it requires that you admit to any type of inappropriate responses or behavior. This log will not only be helpful to you, in court, but it may provide the BPD individual with tangible evidence of their disorder. Do not, under any circumstances, provide the BPD individual with personal contact information, once you have exited. If the BPD individual wishes to communicate, let them do it through a third party, particularly if children are involved!
Finally, if the non-BPD individual chooses to remain with the BPD in the hopes that he/she will choose to get help for themselves in the form of INDIVIDUAL THERAPY, it is imperative that the non-BPD individual find their own personal counselor/therapist to learn positive, reasonable coping mechanisms when interacting with the BPD individual. Remember, the likelihood of the BPD individual actually embarking upon the long, arduous, difficult journey to managing their disorder is slim, at best. Nothing the non-BPD individual can do will fix, heal, help, propel, or, otherwise, cure their friend's or loved one's disorder. The non-BPD individual is only responsible for his/her choices and behavior - they are not required to engage in any behavior or choice that might cause any type of personal damage to themselves, friends, or family members.
Best of luck to everyone in the Real World, particularly those who suffer BPD. Don't be afraid! Get help, be honest, courageous, and BPD CAN BE MANAGED!