Borderline personality disorder is difficult to deal with, whether we are talking about the child who has it, or the parent of that child. This can cause a rift to form between child and parent. I'm speaking from experience, having raised a daughter with this difficulty.
There are good times and not so good times. This does not need to mean that the rift will become larger, nor that it is permanent, though. We are after all talking about our offspring, conceived (hopefully) out of love.
I cannot speak for any other parents, since all people and situations are different, and to lump them all together is just plain wrong, though it is a common method used in treatment. No wonder that the treatment often fails! I can only give my perspectives, which are shared by my wife.
First of all, a parent must understand that there will be times of tremendous mood swings. "Reacting" to them rather than "acting" to them will cause more problems and makes matters worse, for both child and parent. On the parents part, this is the most difficult part, to remember that the things that are said, the objects that are thrown, the actions of the child are not actually done out of anger, but because of a disability.
At the same time, the parent must make sure that the child takes full responsibility for their actions. It may sound harsh, but it is the only way to break away from an already "blaming" society. This is not easy, and it cannot be done during a more violent mood swing. The child must be made to learn that nobody "makes" us feel angry or sad. That is blaming. For a responsible person, we allow ourselves to feel angry or sad. This can be an enormous key in dealing with this malady. As the child comes to realize that they are responsible for their own emotions and actions, it empowers them and gives them more control over themselves.
In severe cases, medications can help. But medications are not a cure all, nor are they good in all cases. Besides being borderline, our daughter has also always been highly imaginative and creative, which often seems to go hand in hand with this disorder. Many of the medications she received either did little to alleviate the borderline condition and mood swings, and many more virtually destroyed her creativity. After trying combinations of 14 different drugs, medical professionals finally deemed that our approach was doing more good than any of the drugs, and she was taken off of them.
Counseling is also very helpful, but again, the counselor is not with the child as many hours as the parent is. This means that for the best results, the parent should actively work with the counselor. In fact, the counselor can do little without the cooperation of the parents. They know this very well. The welfare of the child is well worth the effort, whether we lead hectic lives or not.
Given all of this, borderline personality disorder can cause problems with parental bonding. However, if the parent honestly wants to overcome these difficulties, they can, with a little thought, consideration, and a lot of patience. A parent that does this can very well find themselves more closely bonded to the troubled child than they can with one that doesn't have the same difficulties. This certainly happened to us, and I can't believe that we are totally unique.
Our daughter is now far better, married, leading a productive life, and I must say that we are very proud of her. Love may not honestly be blind, but it does overcome all obstacles.