I think pulling out of your emotional funk without pursuing her is the key. I'm not saying she is having an affair. What we are all picking up on are her recent and 180 character changes... they signal SOMETHING. Whether that is an indication of a relational dynamic change, menopause, a 'crush,' or an emotional/physical affair... nothing at this point should be discounted, until you think you've gotten to the bottom of things. I'm not saying to accuse her.
But if her sex drive stayed relatively consistent during child bearing/rearing years, and she is all the sudden doing this... and she's unwilling to talk about it...