Amy jo has good advice.Therapy would be so good for you.
Vee
Do you have a therapist? Not saying you need one- don't get me wrong, but it sounds like there is more to what your going through than just bipolar. There are some other conditions that mimic bipolar that are not helped with medications- xanax is used more for anxiety- bipolar being mood related.... This may not help but I do know that in my research into my daughters mental health issues that Borderline Personality came up as a possible co-diagnosis or co-condition. It is renowned for the insecurity felt when you are separated from the person your in a relationship with or just straight out separation anxiety and false sense of abandonment from anyone/everyone. Not saying at all that this is the situation with you it just sounds similar. It usually drags the person your in a relationship with into the ground and they end up leaving secondary to the stress emitted from your constant insecurity. Just a thought you may want to talk to someone about the issue not that you may have a different diagnosis.
I am talking in circles, my main point is you really should consider speaking to a therapist or your therapist especially if you really care about this girl.