It is natural for you to feel confused and frightened. The best thing you can do is to take care of yourself during this difficult time. If you're seeing a therapist you may want to discuss the problem with him or her. If you're not seeing someone now might be a good time to start.
I have bipolar disorder and was only diagnosed 8 years ago - (I'm 51 y.o.). Before I started dealing with my illness I put my family through a lot of grief. I was very unkind to my wife to the point where she said go to therapy or else. Hopefully as your boyfriend seeks treatment he will come to see the way he's hurt you and others and be able to rebuild relationships that have suffered due to his illness.