I'm another bipolar with "borderline traits". (disclaimer: the "borderline traits" have not been professionally diagnosed, but if you lived in my head, they would be obvious) My understanding is that there are quite a lot of us.

Your reaction to your friend seems "normal" enough; I think plenty of non-borderline people feel attached, even addicted, to their friends. It's not healthy, but if it happens with just one relationship, it doesn't scream "BPD!!!" to me. Of course, my own borderline side may be making this sort of thing seem more common than it is. ; P

Have you ever had romantic feelings for your friend? Your post makes it sound like he is gay, but our hearts don't always fall for people who might reciprocate. If your feelings for him are a little more than platonic, some of the intensity of your reaction may be explained.

From what I've read, BPD is often misdiagnosed as bipolar. Up to 50% of people with a bipolar dx actually have a different condition, and BPD is often the true diagnosis (unipolar depression and PTSD are other common conditions mistaken for bipolar). And, many people have both bipolar and BPD. Some researchers even think that the two conditions are variations of the same illness. Here is a link to some info on that: http://www.psycheducation.org/depression/borderline.htm

Like Widget, I'd love to see some input on these issues from someone with diagnosed BPD.