Nearly a fifth of couples argue regularly or consider divorce, according to a new report.
A study by the charity Relate found that almost three million people were in "distressed" relationships where they were close to breaking up.
Strains on relationships such as the stresses of parenting and financial pressures have left 1.4 million families at "breaking point", the study warned.
Dr David Marjoribanks, senior policy officer at Relate, said that many couples suffer in silence for years and only seek help when it is too late to save their relationship.
He also warned of the effect that constant bickering and stresses at home could have on children.
He said they are more likely to perform worse in school, have mental or physical health problems and get involved in crime or anti-social behaviour.
Dr Marjoribanks explained that it is not just the actual breakdown of the relationship itself, but the conflict within existing relationships that is the issue.
Researchers looked at data from the most recent UK household study, Understanding Society, to further understand the state of relationships.
It was carried out in 2013-14 and is the most recent year data was available.
The researchers found that 2.87 million people - or 18% of married or cohabiting couples - were in distressed relationships with strains deemed to be "clinically significant" by counsellors.
Relate is launching its first national appeal, Breaking Point, calling for donations to help subsidise services to support families whose relationships and finances are under intense pressure.