I miss how you could always tell if something was wrong just by my music or the look on my face or even the sound of my voice, no matter how much I denied it and said everything was alright.
Emotional cheating, there is no sex, but you go to another person for the emotional connection - maybe you share all your problems and dreams with someone other than your partner.
Causal cheating, there might not be any sex or emotions involved, but you are flirting it up on that business trip when your partner isn't around.