Creamhearts sorry to hear you are struggling so much, and feeling so low.
My best friend suffered from mental health issues, but he hid it from everyone. It only came out when he tried to kill himself last year. He spent 4 long months in intensive care, and when he was awake, he regretted his decision so much. He made a permanent decision based on temporary feelings. There was nothing so bad that we could have helped him through. Unfortunately, it didn't have a happy ending for him.
I can't help but think if he had been open about how he was feeling and gotten help at the time, he'd still be here now. So I think you are being so very, very brave. You're taking such a positive and big step by admitting, even to us, that you're struggling. You're getting help, and that's a huge step.
I have no experience of being sectioned, although I have had mental health issues myself. I don't think you should feel that being sectioned is you failing somehow though. If you were really unwell physically and had to be admitted to hospital, say with meningitis for example, you'd let yourself be admitted and accept the treatment and help without question. Mental health should be the same. It's still an illness, not something you can control. So if they offer you help, please accept it. I know it's easier said than done though.
You sound quite scared and anxious at the moment, but try and focus on the positives. You said your dh is really supportive - that is lovely that you have that. Hold on to it, and let him support you anyway he can. 
Have you heard anything from the psychiatrist yet?