Everybody else will act normal and all prior evidence of their existence will also persist like normal.
I guess for most people it would be pretty much immediately if their significant other isn’t there in the morning and for some fringe isolated cases it might take forever.
I guess best case for me would be around 4 hours on a work day during lunch break seeing a big crowd of people when it would finally click.
Worst case would be probably 5 days when I’m mostly working from home office.
Instantly? Where the fuck is my husband. If only I can’t see him but my twin can I guess me, my now invisible to me husband, and I go to the hospital to ask “yo something is very weird in her brain”
Edit - oh they’d think it’s normal they’re gone.
I guess argue with my twin for hours about my husband still should exist and not have disappeared.