I Want to Know About Borderline Personality Disorder

I met this friend two years ago. If such a thing exists, it was friendship after sight. We were volunteers in the same social center. We used to joke about our "special abilities" : I was suffering from depression, she has borderline personality disorder and we were both former bulimics. It was so amazing to be able to talk about such heavy subjects without being judged. We even joked about our failed suicide attempts. We were not "normal people" and when we were together , I just thought it wasn't that bad. After all, she kept saying: "it makes us special".
Of course, I liked her for many other reasons :she is smart, has a great sense of humor and we are sharing the same interests.
But one day, I received a call from her husband:she had tried to commit suicide during the night. The day before, we had dinner at her place and everything seemed OK.
I replayed our conversations in my head but there were no warning signs.
She left the hospital after 6 months. Since that day, I started to recognize patterns in her behavior. There are times when she calls me and she is full of projects and seems so happy. Then, there are the other days :she ignored my calls or sends me laconic messages.
I really love her but sometimes it is difficult to know if I did or said something wrong or if it's just her disorder that makes her act the way she does. (sorry for my bad English)