Quiet time is one thing, being TRULY alone is another. BPD people can't be truly alone. That means they always have to be in a relationship of some sort. My ex liked to shut herself away in her office, or go for drives alone, or hikes alone with the dogs etc. But that kind of alone is different than the kind of alone where you are not in a romantic relationship. The reason they can't handle being alone is that they project their needs onto other people. They feel like they have a giant void inside of them and this void causes them to feel anxious, lonely, angry, and afraid. The biggest thing about a BPD person is that they are TOTALLY unwilling and unable to look inside themselves to address the core issues that are causing these feelings. It's too painful and difficult and to be honest, I don't even know that a person with BPD has the mental capability to sort all this out even if they wanted to. So instead of focusing inward on fixing their issues, they look externally for the cure. This is why they are often so compulsive with everything from purchases to pets to relationships to jobs. Whatever they are feeling at a point in time is caused by something outside of themselves and they believe ALL their problems will be solved if they could just get a different car, different job, different boyfriend, new pet, new shoes, whatever. Having a relationship is one of the greatest ways they can get their needs met because people are capable of providing them with a lot more of what they need than objects are. BPD people jump from one relationship to another for this reason with no time in between because they cannot handle being alone.
You just have to look to their past to understand their future. They don't change. My ex was in two LTRs before me. One of them was a year. The next was about 2 or 3 years. Then I came along and we were together 6 years. There was never more than 1-6 months MAX between those LTRs. So when she left me, I knew it would be about the same amount of time before she found someone else. I was right. She ended up getting together with a beta male orbiter she knew from before she and I even met. It was super easy for her because he was right there, and beta males make great partners for BPD women because they don't stand up for themselves and offer a lot of attention and forgiveness and service that the selfish BPD woman cannot live without. BPD women often tend to date men who are less attractive than they are because they know their looks will hook the beta male in and cause him to put up with her mistreatment.
I think a lot of people (non-BPD people) sometimes follow some of these patterns to a lesser extent. Meaning, it's easier to look externally for fulfillment and cures than internally. Part of what led me to sosuave and TRP was watching my ex constantly search for external fixes. It didn't work for her and I knew it wouldn't work for me either. TRP is all about being responsible for yourself and making the effort to improve yourself and understand the reality of things. The more time you spend learning this stuff, the easier it will be to understand your ex and leave her in your past.