My goodness Gooby what a time you are having
so glad you found this forum as there are lots of folks here to share your concerns and offer support
I am in awe of you caring for your husband after such an operation - I was there 10 years ago, but was young and only had to worry about myself - not surprising that your emotions are so low
I'm surprised you weren't offered a care package when you were discharged - or was it a few weeks ago
please do immediately contact your Local Authority Adult Services and ask for an urgent assessment of your husband's needs and for a Carer's Assessment for yourself - please tell them everything you have put here, I appreciate you may want to hold back for your privacy but they need to know that you both need help NOW - use these phrases: we are 'vulnerable adults' and 'at risk' and the LA has a 'duty of care'
you should be able to have home care visits - please do accept these, I know it's an intrusion into your home but it will take the physical day to day care off your shoulders - also ask for placements at a day care for your husband (even if he is reluctant to go) and also tell them that a respite stay is needed for you to recuperate after your operation (again, your husband may not be keen, but this is for you to have a break)
sadly, you may have to pay if your finances are above a certain level - but you may not!
could you have a mail box put up put up outside your house, in a place not easily seen from inside, so that all your post goes into it and only you have a key - then you can take out any important items and only post through the letter box stuff your husband can hide without you worrying about it
as for the life assurance - do contact them and ask to speak to a manager or write a letter - explain that your husband has dementia and did not understand what he was doing, he certainly did not understand the implications of stopping payments and would never have done this before his diagnosis (which is proved by the continuous payments) - tell them you are distraught as this policy was giving you peace of mind in your situation (again, let them know how difficult things are) - it is worth a try - and if they don't respond as you hope, go to Citizens Advice for help
I'm glad your GP is involved - please do have a chat with them and lay on the line just how you feel so that they know you need more support - it would be useful for them to make a referral to your Adult Services too
sorry to seem bossy, but you sound so down
very best wishes