the seven-year itch 七年之痒

【例句】
Couples who manage to survive the seven-year itch would be wise not to get complacent.
成功度过“七年之痒”的夫妇不要沾沾自喜。

Those in a serious relationship have long been warned about the dangers of the seven-year itch.
已婚男女要警惕“七年之痒”说法由来已久。