Broken, forgive me if this reply is hugely inappropriate and I'm miles wild of the mark, but something about your husband's 'nervy pain' and the location in the 'front and side of his head' reminds me of something I had about 16 years ago.
I too had an agonising intense pain in exactly the area you describe - front/side of head and yes, it felt 'nervy'. I initially thought I had shingles (it wasn't) but when the awful pain persisted and I was terrified it was something much more serious.
Over the counter pain killers didn't touch it and it was starting to rule and ruin my life. Even to take a step sometimes would cause this shooting pain in my temple. But what rings a bell with me most in what you've written is about opening mouth/moving jaw - as that for me sometimes was unbearable - even thinking about it now makes me go weak at the knees at the memory of the breath-taking agony of it.
Then, on yet another visit to the Doctor's surgery, my regular GP wasn't available and I saw one of the junior doctors, who suggested it might be musculoskeletal, and referred me to the orthopedic department of my local hospital.
I thought this was completely nuts, but I was in so much pain and so desperate I would have tried anything and went for the first appointment. Having described the symptoms to a young female consultant she looked at my head placement, neck, shoulders etc. and said immediately 'yes I can see what the problem is'. She did a bit of manipulation - not quite the chiropractic 'crack' that you see on the youtube videos but she definitely poked and prodded around at the base of my skull/neck and upper spine. The prodding wasn't particularly enjoyable, but not agonising either. Just sore and uncomfortable, and I thought a waste of time, as the pain was in my head and it certainly didn't feel like it had anything to do with my neck.
She told me I'd need a course of physiotherapy treatment (no painkillers were prescribed) and set a date for the next appointment.
Only more or less immediately after that first visit, I noticed that the pain had gone. Completely. With each day after that I remained pain free and in the end telephoned the hospital and cancelled future appointments, because whatever she had done, had to all intents and purposes 'cured' it.
To this day I don't know what caused the problem. I don't know what she did on that first visit other than a bit of poking, prodding and manipulation. But I do know I've never had that 'nervy' intense, agonising headache since.
I realise what happened to me may have no relevance at all with your OP, but what I'm saying is maybe to look at all the options and try not to fear the worst. Pain can be caused for all sorts of reasons, and not all of them are scary. I'm not trying to minimise what is happening with your H - just sharing my story.