The "sex smell" comes from his semen and your vaginal secretions coming together. While he might not have changed anything, things might have changed in you.
You said "umpteen amount of years". Are you close to menopause? Perimenopause? Have you changed birth control methods? Changed your diet?
While men's bodies do undergo changes, they are not nearly as dramatic as the changes in women's bodies.
Since this seems to be concerning to you, don't hesitate to get checked by a doctor. Again - umpteen years. Are you both current with your physicals? This could be a good prompt to just make sure everything is okay.
Have either of you been taking different medications (or stopped a medication) or different vitamins, or eating a different diet? If not, it could be that the smell is still there but your nose is not smelling it any more.