The Seven-Year Itch currently refers to a spouse yearning for something more in life or for someone else in the marriage.
The phrase took on the new meaning with what William Safire referred to as "marital wanderlust" with George Axelrod's 1952 Broadway play. The popularity of the phrase increased with the release of Billy Wilder's 1955 movie, The Seven Year Itch, starring Marilyn Monroe and Tom Ewell.
"That supposed urge for infidelity after seven years of marriage is the meaning we now have for this phrase. It is now often extended to refer to an urge to move on from any situation, and not even limited to those of seven years' duration."
Source: The Phrase Finder
Quotes About the Seven-Year Itch:
Scott Haltzman, M.D. about the 7th anniversary: "If you've come this far, you're already well on your way to beating the odds."
Source: Louise Jarvis. "Love: What Makes It Last." Redbook.com.
Jennifer Nagy: "But the seven-year itch is certainly not a proven phenomenon. Most experts have simply have agreed to disagree ... n my opinion, the ever-changing conclusions indicate that there is no magic number. The studies do seem to agree that couples need to put in the extra effort every day in order to sustain happy marriages. If a couple doesn't prioritize their relationship, their marriage will fall by the wayside -- no matter how long they've been together."
Source: Jennifer Nagy. "The Seven-Year Itch: Fact or Fiction?" HuffingtonPost.com. 1/28/2013.
William Safire: "The phrase is now almost exclusively used to mean 'the desire of a married person to stray from his or her spouse after seven years of marriage' ... Why seven years, not six or eight? Because seven years has a historical basis: in Genesis, Joseph interprets Pharaoh's dream of "seven years of great plenty" followed by "seven years of famine." Farmers who hate hillbilly jokes know about the seven-years' apple and seven-years' bean; military historians refer to the third Silesian war, of 1756-63, which confirmed Prussia as a major power, as the Seven Years' War."
Source: William Safire. "On Language: The Seven-Year Itch." NYTimes.com. 3/29/1992. pgs. 1-2.