Marriage - definition

Shulchan Aruch(E.H. 26:1): A woman is not considered married unless there is a proper Kiddushin. However if the man has intercourse with her in the manner of fornication and not for the sake of marriage – it is nothing. Even if he has intercourse with her for the sake of marriage – but it is a secret – she is not considered married even if she has an exclusive relationship with him. Not only are they not married but we force him to send her from his home. Rema The reason is that she will definitely be embarrassed to go to mikva and therefore he will have intercourse with her when she is a nidah. However if he sets aside a woman and she goes to mikve then some people say that she is permitted to him and this is called pilegesh (concubine) which is mentioned in the Torah (Ravad). Others (Rambam, Rosh and Tur) say that this is prohibited and the punishment is lashes because of the Torah prohibition (Devarim 23:18) of not having a prostitute (kadesha).