I just wrote out a long reply and it got lost, sigh.
Firstly,
read this book (if your pysch suspects you have BPD). It tells you everything you need to know about BPD. What the symptoms are, what it means to have it, how long you'll have it, what will help etc. Get anyone close to you to read it too.
Having a PD doesn't mean you are going to automatically get sectioned. You will only get sectioned if you are a danger to yourself or others and are refusing to go into or stay in hospital.
Typically, a PD stays with people until they are in their 30s/40s, however research has shown that any talking therapy or a hospitalisation will in 60% of people with BPD reduce their symptoms so much that in a few years they will not fit the criteria for BPD, and in ten years most of them will no longer fit the criteria.
A therapy called Dialectical Behaviour Therapy was created specifically for people with BPD.
There are no medications to treat PDs as a whole, they are only used for specific symptoms (such as an antidepressant for depressive symptoms and and antipsychotic for psychosis or dealing with self harm/racing thoughts).
There is a stigma attached to BPD. It's pretty notorious for being hard to treat, and many people get written off as being "manipulative". Unfortunately you will encounter MH professionals who have this view, but there are people out there who understand and will treat you properly.
I have BPD.