Traditionally, when a gentleman and a lady walk together down a street, the gentleman walks on the outside or curb side of the sidewalk.
When a couple is walking somewhere other than on a sidewalk, the gentleman always walks on the lady’s left side. This is the same position a wedding couple will exit the church after the ceremony.
In times past, it was not uncommon for a married man to have an escort for an evening. In this situation, the man walked on the escort’s right side. By doing so, it was very easy for others to identify the woman as his mistress or his wife.