There are checklists usually available online via Tony Attwood or Simon Baron-Cohen. It IS a spectrum and not all symptoms present. How does he cope with change/stress? Can he engage in diversions in conversations or does he want to keep pulling them back to his topic? Does life seem to have to be often on his terms? Has he very specific, borderline obsessive interests? Would you say he "gets" emotions, also consequences? I wonder if he's just feeling a bit rudderless due to Covid and/or empty nest and/or ageing. Have a look at specific websites. The National Autistic Society is probably the best, but these others may have contact sections or support forums. Sorry, I'm a bit rusty as haven't worked in this field for a few years now, but there may be something here for you ,hopefully, or someone else may be along. Oh, take a look at the Minds & Hearts website, lots on there about traits and also partnering. Good luck!