Usually starts out with being co-workers, then moves on to friends, then telling each other their problems, next thing you know they have crossed the line and become dirty lying cheating scum. It's quiet simple ;- Co-workers = stay people that you just work with. Friends = people your partner knows about and is usually friends with also. Problems = talk to your partner or a councillor. Crossing the line = become single if you want to fuck around or grow the fuck up and have some morals.