Infidelity Definition

Wikipedia [2]
Infidelity can be defined as any violation of the mutually agreed-upon rules or boundaries of a relationship, and is a breach of faith in an interpersonal relationship.
Sexual infidelity in marriage is called adultery, philandery or an affair and in other interpersonal relationships it may be called cheating. A man whose wife has committed adultery is referred to as a cuckold, [1] but no equivalent word exists for a woman whose partner has cheated.

Statistics: Prevalence of infidelity

A
27% of people who reported being happy in marriage admitted to having an affair [3].
B
By contrast John Gottman with his 35 years of research into marriage, [4] is reported as saying “Only 20 percent of divorces are caused by an affair. [5] Most marriages die with a whimper, as people turn away from one another, slowly growing apart.” [6]

[1]cuckold
[1]pronunciation
[1]definition

[2]definitioninfidelity

[3]Clinical Psychology resources on infidelity

[4]Gottman’s Sound Marital House Model

[5] Rescuing Marriages Before They Begin

[6] Women’s Infidelity by Michelle Langley BOOK(ISBN 0-9767726-0-4) Straight talk about why women have affairs, 2005