The prohibition of kirva (coming close) is to protect a person from having relations with someone prohibited to them. The main elucidation of this mitzvah is in the Sifra, as well as the Avos D'Rebbi Nosson. There is a machlokes (disagreement) as to whether the prohibition of kirva is a Torah mitzvah or a Rabbinic mitzvah. This prohibition involves the categories of the senses of touch, speech, dress, and smell. The two reasons given for the harchakos (distancing actions) during the nidah period are to protect a person from having relations and to proactively remind a person that their wife is a nidah. There is no reason to be embarrassed when others happen to see that a couple is following the halachos of harchakos.