Most people have equated the word "issues" with infidelity when "issues" in a relationship go far beyond cheating. Becoming addicted to being on any site (including this one) is an issue within a relationship if one's partner is being neglected, is feeling left out, is being ignored due to their partners participation online or he/she is being deprioritized over interaction on the site.
So yes, I think that facebook and other sites can indeed cause issues in relationships. I also think gaming can cause issues in one's relationship as well. It's like how any "addiction" can come between two people when it causes an emotional dis-connect.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion