My last post came up with only half of what I'd typed and previewed, and with a broken italic not present in my previews, at the fifth post down and with Tannywheeler's post after mine. A re-post got vaporized in hyperspace.
Traffic must be heavy.
What my back button says I posted was (third try):
If you set aside the same day every week for something special/get out of the house/whatever...
And then you hear:
"But we always do that. I want to do something SPECIAL once in a while."
It depends, of course, on both persons involved; but often it comes down to
"The I Don't Know What I Want From You, But I Ain't Gettin' It Blues."
(Ginny Reilly)
It is possible that Clinical Depression, or the response to CD in a partner, may be present? If so, you can try; but it likely ain't gonna help without medical intervention. It's probably more likely that it's just boredom, but it may be boredom with the partner as much as with what the couple is doing - so still a potentially serious situation.