Facebook is cited as one of the reasons for divorce in a fifth of cases, a law firm has said.
JCP Solicitors, based in Swansea, also found that one in 10 couples blamed the social network as the main cause of divorce action.
Reasons cited included inappropriate messages or photos sent to members of the opposite sex, posting nasty comments about a spouse and friends reporting a spouse's online behaviour.
Christine Rawsthorne, a family solicitor at the firm, said: "It used to be the telltale lipstick on the collar. Then there were the giveaway texts which spelled the death knell for many marriages. Now it's Facebook.
"Ten years ago, it was probably unheard of for a divorce petition to refer to one spouse finding out about the others infidelity on a social networking site. However, when you consider that Facebook has around 750,000 adult users in Wales alone, some might say it's hardly surprising that some of those people will be using it to contact an old flame.
"The perceived safety of sitting at a computer screen to contact someone you would otherwise have left well alone is leading to many petitions for divorce being filed with county courts throughout Wales.
Innocent intentions turned ugly
"Facebook and other social networking sites are not only being referred to more frequently in divorce petitions, but people's postings on such sites are often being printed off and referred to the court in cases concerning children.
"A client may do their best to portray themselves as a reasonable and responsible adult, yet they go on to post abusive or threatening messages to their ex-partner through social media."
Rawsthorne said that once comments were online, they would be there forever - even if a post were deleted, data retrieval means most records can be found.
"In the end, Facebook is a social tool. However, even the most innocent of intentions can turn ugly with improper use. Remind yourself why you're using it and regularly assess your intentions with the people you're frequently communicating with.
"Facebook may not call itself a dating website, but hundreds of millions use it to connect on varying levels. Intimate conversations, even online ones, should only be reserved for your significant other."