She's turning me into a wreck... I don't know what to do...

This sounds really complicated. I have a family member with the same issue, and unfortunately the only solution I found to minimise the emotional damage caused is to keep my contact down to absolute minimums. I wish I had some advice for you that could help get through this in a positive way, but either you need to just accept the pain that she will cause or you need to decide it's too much for you and move on. Being the subject of the abuse that such a person can throw out can be extremely demoralising and really harm your self esteem unless your willing to put yourself above it.

 

Any relationship with someone who is mentally unstable is going to demand from you a huge effort and patience, also being ready to handle their crisis.
I don't know everything about BPD, but I've met people with that disorder, and I have the impression that the sickness affects people in different ways, so you could say there is different "shades" of BDP. Good signs are that she can work and afford to pay for her own place. This is at least an indicator that she is actively trying to keep herself above the water, instead of expecting everybody to help her.

I won't tell you to run away inmediatly, because of what I just told you : If she agrees to try to keep a job and pay for herself, and if she is trying to make some effort to change her ways, I think it could be worth it, if you really love her.

Be careful if she appears to excuse her behaviour on a sickness and refuses even to try to keep a job. That is called manipulation, and a one way ticket to emotional and financial disaster.

I also advice you to detach yourself emotionally from her when you sense one of her storms coming. You know it's not her, but her sickness talking to you. It could be also good to try to look for some form of therapy yourself, or a group for people who is with BPD affected people.
It takes years until you learn how to cope with BPD, and your 20s are not precisely your best years when you got that beast kicking inside.

 

I'm sorry to hear you're both going through this. You can't rescue her because it goes too deep, but if she is willing to also get professional help, then there is every chance that she can learn to manage the impacts for your relationship. Would she be willing to? This is really important because is she isn't willing to then you're going to be in for an ongoing battle.

To answer your question, no it isn't okay for her to treat you the way she does when she is having an outburst. This is where boundaries need setting and is the difficult part because it will require her to take responsibility. It will help both of you if she understands that you are not responsible for her, nor should you be a verbal punch bag. When this happens she needs to know that *example* isn't acceptable because it hurts you. So with this in mind, try not to get caught up in arguments that you wont win, or reinforce negative behaviour by pandering to her. Be supportive, but also firm and consistent.

I'd definitely recommend finding a support group or therapy, as another poster said. If that's not an option then get a book/s on living with someone who has this.

 

It's very difficult maintaining a relationship with someone who suffers from BPD as there are so many extremes to deal with and you experience a lot of emotional manipulation. One minute you feel intensely loved and cared for and the next you are utterly despised. There is no moderation and you end up riding a very fast rollercoaster that drains you completely. Ultimately, it can damage your own mental well-being and you need to be very vigilant to the signs that you are no longer coping with it all. Do you feel as though you are reaching that point?

It's good that you are understanding and caring, but it's important to remember that you are not responsible for your girlfriends feelings or actions, despite any claims she makes to the contrary. Keeping this in mind can help to some extent.

If you decide to keep at the relationship you will need to be very firm in setting boundaries and you absolutely must stick to them. If you say no, you must mean it. If you say you will do something you must follow through with it, without hesitation. If boundaries have been difficult so far, it will be very hard initially, but if you give into outbursts it will only reinforce the borderline behaviour and escalate the problems in your relationship.

People with BPD often have self destructive tendencies and it's easy to fall into the habit of coming to the rescue. I don't know if this is the case in your relationship, but it's not a good idea to rescue. It's difficult to stand back and do nothing, but if you are living with someone who has BPD + destructive tendencies you really need to be strong, otherwise there will be no incentive to change the patterns of behaviour and dependency issues will increase.

Be warm and kind, but also be honest. If your girlfriend has an outburst against someone/something and it's not rational, be prepared to tell her. It may not be the easy option as you may end up on the receiving end yourself, but it's really not a good idea to encourage extreme responses. Doing so only makes things worse.

Do you feel strong enough to set boundaries like these and stick to them? If not, you may need to seriously consider moving on for the sake of your own well-being. It will be very hard to do as you are so invested in the relationship and it would most likely lead to an explosive reaction, but if you arrive at the decision to leave, you must not turn back. Think about it carefully, but before you make any decisions you may want to check out this recommended book:
Stop Walking on Eggshells: Taking your life back when someone you care about has Borderline Personality Disorder

If your girlfriend can be persuaded to seek help from a therapist who understands and works with BPD it could save your relationship. There are treatments that have been proven to work. You may also benefit from some individual sessions with a therpaist while you are struggling with all of this or check out support groups for family/friends.