Honesty is key with an FWB relationship. I always let my FWB/Dom know if I'm startig to date someone and we have a written contract that if we start to date someone seriously we will let the other know and the whole thing is off. If we are dating someone casually, we don't have sex with them until it gets serious so that the FWB and the romance don't overlap sexually. And the romantic interest is always aware of my FWB and knows our contract.