Very sad situation, but agree with Esspee.
There’s no such thing as ‘a common law partner’ - sounds cruel after all the years you’ve spent together, but in the eyes of the law - you’re just playing house together.
Was there a reason not to marry 20, 10 or even 5 years ago?
Having re-read the OP, I also see he didn’t get round to writing a will either - another lesson to be earned by others in the same position. Not to add to your anguish at this time, but I hope you (or your son) will be the beneficiary of his (vocational) pension and not his ex-wife! I definitely wouldn’t be paying for the funeral, but with Covid it may be very different to what he wanted anyway.
It may be worth spending an hour with a solicitor, but moral and legal are unlikely bedfellows.
You have my sympathy ?