Does Sex Have a Use-By Date?

Recently I was approached by a writer working on a column for a dating website. She was curious about "sexual newness" which I understood to mean how sex feels at the beginning of a relationship, and what couples could to to prolong that feeling and stave off "sexual staleness".

I'm not sure what she thought of my answers (I'll have to wait and see if I make it into the article) but I found the questions fascinating. I was particularly interested in this idea of sex going stale.

What does tha...