This might increase if you do not emotionally respond to them; that is, if you do not hop on their emotional rollercoaster and get upset as well.
One way to help control their extreme behavior is to learn your own boundaries.
This might be easy because the person with BPD may push the limits of your boundaries.
Once you learn your boundaries, you can set limits: State what your partner is doing to push your limits, and note a consequence if they don't stop the behavior.
To establish trust and influence in your partner's life, complimenting your partner for even little things they do that are noteworthy may surprise you and go a long way.
You can also use compliments to reward good behavior, such as "I know you were stressed out yesterday, but you handled it really well," or "I noticed the way you have stopped yelling at me." However, note that you need to assess what mood your partner is in.
You need to earn money so you can buy the things you want." A person with BPD does not have the same understanding about emotions, and he lacks coping mechanisms to manage them efficiently.
You need to have a realistic understanding of your partner's behavior and your role in his life as "caretaker." Also, you also need to keep in mind that your partner may never learn to meet your emotional needs. Your loved one has to be committed to healing himself with the help of therapy.
Another unfortunate aspect of BPD is that people with BPD act in a manner that lacks empathy for those around them.
For instance, if your partner threatens suicide, you could say, "Okay, I'm calling the police." Hopefully, this will be enough to have them settle down, and if your significant other does not settle down, at least you will have the help you need to handle the situation.
Suicide attempts are a common feature of the disorder.
Realizing that your loved one has a completely different emotional perspective will help you protect yourself and stick to boundaries.
With BPD, knowledge is power, and if the person doesn't know that he has the disorder, and the people around him don't know it, they don't know why their loved one is acting that way.