I am very interested in how a situation like this would pertain to an exception that Jesus mentioned regarding divorce.

Matthew 5:32 (Amplified Bible)
   
But I tell you, Whoever dismisses and repudiates and divorces his wife, except on the grounds of unfaithfulness (sexual immorality), causes her to commit adultery, and whoever marries a woman who has been divorced commits adultery.(A)

Is it considered adultery or at least sexually immoral if a married person is secretly seeing someone outside the marriage.  Acts may involve kissing, making out, excessive phone calls and emails.