Emotional Ups and Downs

My fiance has been on a wild roller coaster ride lately. Some days he is fine, but the next day there will be a trigger and he spirals down, often taking me with him. This weekend, while still reeling from a meltdown, he slept late and was so devastated he refused to get out of bed. Saturday was a struggle, but we got through it because I encouraged him to work on one of his hobbies. This seemed to stabilize his mood for the next few days.

Today, I got a text from him. He's an academic and today he heard back about a very important grant he applied for. He didn't get it. He doesn't need the money, but this is a confidence thing. He is so full of self-doubt at times that it crushes him. I have no idea what he is feeling right now, but I'm mostly on here for me right now. These mood swings scare me. They make me want to jump and run. Right now I feel sick because I am so worried about how is reacting to this. I have no idea how to keep going or how to help him. I feel so empty right now, I don't know if I will be able to give him the support he needs if he doesn't find a way out of the negative spiral on his own.

I don't know. I'm just sad and worried and I have no clue what to do.