Welcome paco
I don't know what to do, this leaving and coming back together is killing me. I don't know what to do. This situation is affecting me deep inside me. I am beginning to be worried about me, my mental health.
You have a good start in being worried about your mental health, also it has a direct affect on your emotional and physical health.
The push/pull behaviour you are experiencing is devastating to your self esteem and confidence; PWBPD push you away when you get too close and pull you back when you are too far away, this is of course totally opposite of what you know of basic human nature. BPD is a very serious mental illness, and sadly it is a disorder that protects the person who has it from emotions that are too painful for them to process: they feel intense shame and something like a slight criticism that would barely affect you, will cause a PWBPD to feel so low and unworthy of love that they must rely on their psychological defences to avoid their intense feelings.
Keep reading and learning, you will find that most PWBPD don't want help, blame their partner and ex.'s for their problems (common for them to be the poor victim), and remember that unless a person truly wants help, they will not get it.