In my assessment, there is a distinction between cheating with someone you know, and a WL. That said, I imagine it would be lost on your partner. The distinction is emotional attachment.

I suspect that using a WL whilst staying in a relationship is common, with the root cause being a mismatch in libido. Cheating with someone you know will involve emotional attachment, which I'd suggest indicates the relationship is dead.

Using a WL while in a relationship is sad; but at the end of the day, purely functional. A full-on affair is much more. I expect that is the mindset of people who do not regard using WLs to be cheating. And that point of view is not without merit.