The secret couple has discussed marriage issues between him and his wife, let's say they even talked about going on a secret trip together or something, and they even went on dates alone together but keep in mind during this whole time nothing physical happened because of the boundries.
Its cheating b/c of the secrecy. That is one of the hallmarks of infidelity. Also the inappropriate boundaries. Tho, personally, I wouldn't consider it the same as full-on affair = emotional + physical. But the emotional connection is usually how it starts.