She truly cannot believe that two people who really love each other could ever really split up simply because of such a trivial thing as a large imbalance in their level of sexual desire.
Welcome aboard, MM.
Usually IMHO it's not the absence of SEX as such (meaning IC) but a lack of affection, physical gestures during the day, sexy remarks, kisses, holding hands, snuggling, etc. that is the hallmark of the SSMs that we talk about here (and live). There's the feeling that our partner just doesn't find us physically attractive, has lost interest in our bodies, has lost interest in giving/receiving pleasure in a sexual context.
MM, does your wife do any of these things? Or have these gestures gone by the wayside, too?