R.S is correct. In Orthodox Christianity sex outside of marriage is forbidden. Also, if you do not go church for 3 weeks and you are not sick or something you are automatically excluded from the church. This is how strict rules are. But, like SuperMantila said, very few people play by the rules (including me). We can see the results..broken families, depression, suicides..
I will tell you this..in real life people I know broke the rule..he was a priest..bad, very bad thing happened, the worse possible..