The concept of monogamy isn't one recognized by the unicorns. It's common for unicorns to have more than one partner.
Horns are often rubbed together as a form of physical affection (platonically and romantically).
Unicorns do not have a concept of gender and gender roles.
Unicorns don't typically wear clothing. Clothing is usually reserved for special occasions, bad weather, and situations where the extra protection is needed.