You have a very interesting situation..
Few red flags for me was.. "Unhappily" married.. If its one thing I have found in my 8 years of this.. women that are unhappily married are just looking to have a bit of revenge dont be the easy target.. Not all of them are that way but its never a good place to be.
My wife and I tell eachother everything.. truth will set you free bla bla bla! if this is in your heart of hearts.. tell your wife trust me she may be hurt but if she loves you for who you are she will understand.
Besides you can never really know if she feels the same way
I keep in touch with a few of my exes.. but the saying goes.. they are exes for a reason be careful of bringing up past emotions that will cause trouble in the relationship that matters most to you right now