For them the alternative to an affair is a conspiracy to overthrow the US government. It is their cover story. Why else would they talk /text so much?
I think it is both. They had an affair and conspired to overthrow the US government,
I would be suspicious of any FBI agent in any contact with Strzok and Lisa, who I believe intended to place an agent close to Trump for very bad action. Their smugness alone indicates they still believe they have power.