Affair may also describe part of an agreement within an open marriage or open relationship, such as Swinging, dating, or polyamory, in which some forms of sex with one's non-primary partner(s) are permitted and other forms are not.
Participants in open relationships, including unmarried couples and polyamorous families, may consider sanctioned affairs the norm, but when a non-sanctioned affair occurs, it is described as infidelity and may be experienced as adultery, or a betrayal both of trust and integrity, even though to most people it would not be considered "illicit".
When a romantic affair lacks both overt and covert sexual behavior and yet exhibits intense or enduring emotional intimacy it may be referred to as an emotional affair, platonic love, or a romantic friendship.
An extramarital affair that continues in one form or another for years, even as one of the partners to that affair passes through marriage, divorce and remarriage, could be considered the primary relationship and the marriages secondary to it.
He should be telling her, with the warmth of her body warming his, that his second wife had confessed to greater sexual pleasure when she remembered that she was deceiving him.” ― William Trevor “In a sudden and soundless eruption, as if he has fallen into a waking dream, a stream of images pours down, images of women he has known on two continents, some from so far away in time that he barely recognizes them.