What you describe sounds very normal to me, unfortunately. I've heard "the only way out is through," but them being dead is forever, so it's kinda more like, "the only way through is through." You WILL feel more stable eventually. But it takes a very long time. (It's different for everyone.) And sometimes you'll feel a tad better only to feel worse following that.
As for feeling like you can't survive it, I'm sure many/most of us were there, though I honestly (mercifully) can't remember much of the first five months (and, like you, I lost a lot of weight). It feels physically unsurvivable. I always call it "bearing the unbearable."
Do you have a therapist? I strongly advise it. Working through things you've learned afterwards gives you even more to work through and resolve. There's loss, there's trauma, there is new information, there's just so much hurt. I can't emphasize enough how much I leaned on having that time to just empty the contents of my raw feelings in therapy. I credit lots of therapy early on with helping me heal more healthily and long-term. It also helped me to write, get it all out, I needed to get it out of me, and it was an ever-renewing spring of pain and sadness.
I tried to get sunlight and be active - I knew that my insides were a very dark and complicated place, and I needed to counteract that as much I could with simple, basic, good creature stuff like sun and endorphins and sleep and hydration.
I'm thinking of you, and I'm so sorry for all you're enduring. You will survive this. We are all next to, ahead of, and behind you on this path. I used to look at the first widower I met after losing DH, and chant in my head: "If he survived it, I can survive it."
Edited to add: From what I do remember, the first few days/weeks contain the worst feelings I've ever known or imagined. You're not crazy for feeling so bad (maybe you're not wondering that, but I was). It's natural.
