Marriages get ruined for lots of reasons and its possible to meet people in lots of ways. Many of them KOSHER
I know of someone who hired a nanny and eventually divorced his wife and married the Nanny. People meet others in Shul , Offices , Business trips , other business outings like lunches , meetings etc.
To blame FACEBOOK for failed marriages is just ridiculus and trying to assign blame where it doesnt belong. YES there are marriages that ended because of facebook, but its not any greater than other ways to meet a person. and probably less.