Wow, I just read your post and it makes me very very happy. I may only be 21 but I believe in Love more than anything. My bipolar has ended 2 two year long relationships for me. For the longest time I felt, admit-tingly still do, that my bipolar makes me unloveable although I have great, true love to offer. Gives me hope that the right person will love me despite my issues and be mature enough to handle them.

My Advice:
Make sure to tell her you love her every day if nothing else. Maybe even surprise her with flowers. Tell her you will stand by her through thick and thin and support her and that her bipolar is not burden on you (if you feel that way of course) because I know that from now I'm going to be so afraid of someone getting sick of a "dealing" with me. I feel guilty that someone else has to deal with MY mood swings. I see myself as a burden at times. Maybe she thinks you deserve better. And if you have told her all of this say it again until she believes you.
You need to find out if its the bipolar talking or if she honestly doesn't see the relationship going further. Be accepting of either. Thank you for taking the time to read up on bipolar. You seem to be the kind of person someone experiencing bipolar needs in their life...Understanding. I hope it works out.