My dear friend, I have the same exact problem (I'm also a borderline, BTW). I end up sharing the most intimate details of my life with almost complete strangers. I have read tons of BPD literature, and they all concur that borderlines tend to have a hard time keeping personal details private. We tend to share intimate details with people, for many reasons:

1 - We have a strong need to be heard, especially when we don't have a therapist (like you mentioned).
2 - We have a need for "instant intimacy" (this is very common), and have this illusion that, the more we share, the more the other person will share, and we will become closer as a result of this sharing. However, have you noticed that, when we share a lot of details, the other person (typically a non) doesn't share the same amount of info, and we get disappointed, and we think that they're not interested in us. Ever feel this way ? This is me in every friendship/relationship.
3 - The inability to control emotions, which pretty much defines BPD, means that there is no protective cognitive mechanism that would say "STOP, don't tell him that, because he will treat you differently, and he will write nasty messages on your Facebook page". In other words, we easily get carried away when we start to have a pleasant conversation with someone. There's no safeguard to protect us from saying too much.

I hope what I said makes some sense. You seem like a wonderful person. Feel free to PM me, anytime.

Have a great day/night