I do not think it has actually been said that Anthony is Steph's father but I think it has been obvious for weeks now that he is. I do think it is fear of Anthony that is holding her back from telling the truth, nor can it be that she does not want to spoil Steph's relationship with Anthony, indeed on the contrary I would have this should be a priority. Her relationship with Caleb has been destroyed, while the truth could save it. The only power Anthony has is that he thinks she is having an affair with Cain, but unless Ruby or Cain admit to a one night stand, they can deny this and say Anthony is making this claim to be spiteful. Mind you Cain's behavior is not helping.