I'm wondering if there's a proper term to describe the partner with whom someone cheats.
I am not married. I had an affair with Caitlin who is married (it was one time and it didn't mean anything). Caitlin is an adulterer/adulteress but what would that make me?
"I don't think it's fair for me to be forever branded a ____."
"I don't think it's fair for me to be forever branded the other man/woman."
More formally:
The person an adulterer has an affair with is the third party.
other man (n.)
A man with whom a married woman has an affair —usually used with the
E.G. Marshall plays a man who, believing himself cuckolded, plants a bomb in his own basement to destroy the Mrs. and the other man. — Mike Flaherty m-w
The lover of a married woman or female partner. Lexico
other woman (n.)
A woman with whom a married man has an affair —usually used with the m-w
The female lover of a married or similarly attached person.
Her husband left the matrimonial home to live with the other woman. Lexico
third party (n.)
A person or group besides the two primarily involved in a situation, especially a dispute.
the involvement of a third party as an independent valuer Lexico
"Adultery: What About the Other Woman (or Man)?" Looking at the ethics of adultery from the other side... psychologytoday.com
Question
Can I sue the other woman for destroying my marriage?
Answer:
This is a very common question, but a pretty uncommon scenario. Depending on where you live, you may be able to file suit against the other woman (or man) through one of two types of civil tort claims – "criminal conversation" or "alienation of affection." Lina Guillen; "Can I sue the other woman for destroying my marriage?", divorcenet
Whilst some people call a close friendship between a married man and a female more than questionable, others define "being unfaithful" only as having actual sexual intercourse with a third party. Petra Falk; Being the Other Woman: the Complete Hanbook for the Woman in Love with a Married Man (2009)
In general, society looks at the other man or other woman as being the responsible party in an affair. It’s understandable that they become the target for the rage and anger the deceived spouse feels. Cathy Meyer; "4 Tips For Dealing With The Other Man or Other Woman", liveabout.com
It is generally recommended against naming the third party – it can greatly raise tensions, as well as costs and timescales as there are more parties in the proceedings. It has been far more usual practice for Petitioners to refer to adultery being committed with an unnamed man or woman. Wedlake Bell; "Naming the third party in an adultery application for divorce"
How Do We Define Adultery?
... We might start by saying that what is called for are two relations, that between a man and a woman who are married to each other, and that between one of these two and a third party, who might be married, or single. Edward Gallafent; Adultery and the Female Star (2018)
For instance, Gn 38:24 defines a betrothed woman's sexual intercourse with a third party as adultery deserving the death penalty (see also Dt 22:23). A. Abasili; The Understanding of Adultery in the Hebrew Bible (2016)
Respondents will often give acceptable evidence anyway, and this is especially so if by giving the confession the respondent is able to keep the name of the third party involved out of the suit, as is now the norm.... Frances Burton; Family Law (2003)
It's also extremely unfair to the third party involved in the affair who oftentimes gets hurt. E. Guevara; Unveiling and Conquering Adultery (2020)
If the offending spouse is believed to have had an opportunity to cheat, and if s/he seemed to be intimate with or fond of a third party, the courts could consider this as adultery.... S. Sahni and G. Jain; Internet Infidelity (2018)
Homewrecker is pretty good. Mistress works, but only for a woman, unfortunately. You’re looking for a word for a male mistress. Gigolo or hustler if money was exchanged. Whore can be used in a strong derogative sense quite effectively for either gender. Good luck!
Adultery will do.
Here's the definition:
sex between someone who is married and someone who is not their wife or husband. — Longman
As it is "between", for both who committed such behaviors, it's called "adultery".
Those who commit adultery are adulterers.
