Mean bipolar boyfriend, depressed me:(

My very kind very loving happy boyfriend had a switch go off in his head just 5 days ago. He has been having these mood swings that we are almost sure it is bipolar. Like ultra rapid cycling mood change a few times a day. It was triggered by a stressful event involving me, (I made a mistake, but it wasn't the end of the world) and in his "down" moods he has been blaming me for the worst time in his life, all his horrible feelings that he describes in detail. I am why he wants to give up. (Even though Im the only one he's talking to about these feelings I'm the only one who is 100% there)

his two moods conflict, normal him saying sorry for what he says when he is down, which makes me feel great. But yesterday, the angry part of him told me the nice things he said to me might not have been true. That was so so awful. I was reading something nice he sent the other day to make me feel better and now I cant bring myself to look at or think about it.

I coach him through his bad moods and he is going to the doctor for month long treatment in a few days, but will still have contact with me. I can't handle being treated this way by someone I love so much. I'm so scared he will hurt himself.

I'm taking my antidepressants on schedule but this is really tearing me apart. I'm going to still be there for him and support him, but I need help desperately. Any advice?