With the decluttering... sometimes it helps to have a friend help out with this. (I've gone to friends houses and helped them do this... filling out a huge trash bag or two, or filling the back of a car or truck with stuff for donation). Having an outsider can make a bid difference. And even if you don't have any friends available, you might be able to hire someone to help with this. I tend to collect things, but have learned to "shed stuff" and de-junk my home over the years. It does feel really good! Like losing weight!!!!
But don't do it just for your husband, do it for yourself.
I can't blame you for feeling uncomfortable about your husband's FF. We can't always change our husband's choices in something like this, but make sure you have a great network of friends too. Maybe both female and male...
There is no arriving, ever. It is all a continual becoming.