I am bipolar and I have a fifteen year old son with bipolar. Your boyfriend swings from depression, to gradiosity to paranoia.
Those are all symptoms, the frequency doesn't matter. I would suggest that you speak with a psychiatrist and tell him everything you have told us and see what he thinks. It may be the best $200. you ever spend. Because living with someone who refuses treatment may be the most difficult thing you ever do. You love him, but like any other mental illness, it is up to him to want to be helped.
And if he refuses, is this how you want to spend the rest of your life and do you want to bring children into this mix? These are serious questions you need to consider. Breaking up is painful, I know. And breaking up with him may feel like you are abandoning him, but if he is refusing treatment, he is on his own anyway. He is incapable of loving you the way you deserved to be loved when he is so sick.
Good luck to you,