I have been with my girlfriend for about 5 and a half years now and I now live with her and her family. I hope this doesn't offend anyone but I'm going to post my personal experience with her sister from the family's side (I'll go with Sam for her name. Don't want to use her real name) 

Sam is 22 and is literally the nightmare that a lot of people with BPD are afraid they are portrayed as by the media and medical community. 

When I first met my girlfriend, Sam instantly became jealous and saw me as someone who was taking her sister away from her. She would make comments within a month of meeting me that she wanted to "punch me in the face" when I talk because it makes her so angry to see her sister have something she doesn't. This anger at us being together turned into her vigilantly trying to make sure our alone time together sucked. She will check for locked doors and if she finds one she will start slamming doors in the house and yelling. She once heard us having sex after being together for 2 years and she literally ignored us for over a week out of anger and told her sister she is a gigantic slut (My GF was 20 years old at the time and I was only her second person) She wouldn't even acknowledge if we were in the same room as her. After this happened, she figured out how to pick the lock on the door so whenever we wanted privacy we would hear a click and go "yup, Sam unlocked the door again".

Throughout the years there has just been this constant anger where anything could set her off. A big trigger for her is any kind of criticism whether it's constructive meant to help. Over the course of five years we have not been able to get Sam to look at herself and her own actions. All she can see is what everybody in the world is doing wrong. She won't see therapists anymore because she just ends up hating them and is convinced they are just huge assholes when they get to the part of working on yourself. For instance, she will come home from work angry that someone asked for help on something. She works at a food place and when they get slammed she refuses to help because " she was hired for a dishwasher, thats not her job". If you were to say anything that even remotely said "You work at a food place and it is your job to do anything you can to help the customer" she will literally be on her way to the car telling you to fuck off before she gets in and peels off. 

There has been no improvement in any areas of her issues whatsoever and it has made life for everyone in this house so hard. She absolutely refuses to help out with house work and when it comes time to do something as simple as cleaning the bathroom for the first time in a year she resorts to simple manipulation and will all of a sudden "feel so sick she's going to die". This is pretty much her way of saying she is avoiding responsibility and if you try and call her out on it there will be hell to pay and doors slammed. This is her most used manipulation technique. She doesnt have the intelligence that a lot of people with BPD have so her manipulations are very repetitive and simple. She will use this for almost any situation. If we're running errands and she decides she wants to go home she will just get a sudden stomach ache and you need to drive the 5 miles out of the way to take her
 home then finish your errands or you're gonna face the rage. If you are ever not feeling well she will try and help you to the point where it's more of a hindrance. We have come to learn that this goes hand in hand with her manipulation. She tries to help any time someone is sick because she expects you to drop everything and let her do whatever she wants when she says she's sick. I guess this kind of justifies herself in her mind to get her way by claiming she's ill multiple times a week.

It's so hard to try and help at all because the second you will try to suggest ANYTHING she responds with all the anger she has and leaves the premises immediately if you keep trying. It's affected every aspect of her life and she is miserable but the one thing she refuses to do is ANYTHING involving actually fixing the issue. At this point, we are pretty much in the same house just avoiding her as much as possible because she has shown over and over that she won't accept help. She just wants to do exactly what she wants when she wants and will not be told what to do by anyone. Sam is literally the biggest selfish asshole I have ever met (I'm not saying all of that is from BPD) and even her family thinks so. We still show her love and support as much as we can but it's to a point where everyone is bowing to Sam's wishes all of the time because we're tired of it. When you want to shower you can't do so without going through her first. If she decides she wants to shower while you're in there she will start banging on the door yelling at you to get out. She literally just decides what she wants and bullies her way into getting it at all times whether it's the last serving of food or getting to use a part of the house. All of this combined with the fact that she does nothing to contribute really fucking sucks.

This selfishness even applies to good things happening to others. If you get a new job or a promotion we have to get together and figure out how to break it to Sam. She absolutely gets PISSED when good things happen to others. My girlfriend was recently laid off and when she got a new job we had to wait to tell Sam until she was in a great mood. Her reaction to her sister no longer being unemployed? "God, nothing good ever happens to me. My sister has it so easy."

She refuses to learn new things. When she wants something done and she doesnt know how to do it she has decided that others will do it for her for the rest of her life. She won't learn how to do her simple taxes using a program, she won't download her own music, she won't take care of her car or even check her oil. It doesnt matter how simple something is, she just refuses to put in any effort. If you tell her you're only going to help if you can teach her so she can be more self relient, you get the anger response and something along the lines of "fine! I guess I just won't do my taxes this year then!"

The issue presents itself in any and all conversation involving her. When family come to visit, any time anyone tries to say anything she instantly cuts you off and says "oh that reminds me of this thing that happened to me let me tell you all about it." You could be trying to discuss how you're going to fight your cancer and end up having a conversation about her minor surgery she had years ago and how hard it was on her. Once she has said what she wanted to say she will just leave the room so there's no way to make it a two way conversation. If she is not 100% interested in something you have to say she won't even pretend to listen. You could warn her of the dangers of not getting your oil changed and when her engine blows she will have no idea it would happen because she sat there actively ignoring you every time you brought it up. She will then use this to place the blame away from herself. How could she have known her engine would blow when no one told her? It will then now become our sworn duty to make sure one of our cars are available to get her where she needs to go because unforseen circumstances happened to her car. This is always followed by "why do all these bad things always happen to me!?"

Does anyone have ANY ideas on how we could talk to her or improve things? I have suggested numerous times holding her accountable for her actions but nobody seems to want to deal with the tantrums that will be thrown if she doesnt get her way. I'm really sorry if this sheds BPD in a bad light but this is just the tip of the iceberg with what we are going through with Sam. It is how she is and it is what we are dealing with. I really think that on top of BPD she is just a selfish person and the two have combined to make a nightmare. I know not everyone with BPD is like this. I appreciate any help or ideas.

I have only included the big issues that are making day to day life difficult. I realize this may just make her look like a narcissistic person but her fears of abandonment and other issues don't really carry over into our daily house life as often as her anger and emotional outbursts and what not.
