In summary, the more the better.
Regardless there is still a lot to be learnt from observing the way partners speak, touch, and generally relate with each other.
Having said that, this is what the regularity of sex says about your relationships:
This is “typical of a very very very happy relationship – relaxation/honeymoon ecstatsy.”
“Typical of a very happy marriage.”
“Typical of a harmonious marriage, especially in working couples.”
“Typical of marriage experiencing pressures of life”
"Typical of a disharmonious marriage, especially life in-between quarrels/storms."
"Typical of a marriage in co-existence – uninterested in each other."
"Typical of a marriage in serious disharmony – unfaithfulness/adultery."
"Typical of total breakdown of marriage and virtual divorce."