From what I gather, Sasami and Kamiomi will not get together because Tama exists, from which Tsurugi/Amaterasu herself claims to be the next in line for her power, when it's traditionally to be the female child product of an incestous brother/sister relationship (aka. supposedly Sasami/Kamiomi's child).
Or maybe it's because I'm slowly inching towards boarding the TsurugiXKamiomi ship that I'm thinking that way.