Depends. On what the pair is. A pair of socks never have sex and that's fine by me. A pair of monkeys might monkey around all day and night long for
days! If it is humans you are asking about then I guess they should make some kind of intimate contact daily be it nature or otherwise.
My advice for you and your girlfriend is to quit speculating and learn from one another. 'Pairs', not matter what they may be, have their own drive
and reasons. You are not going to find THE answer to your question anywhere outside of your own self you are paired with..No, not even ATS!

Mags