act II scene I how have oberon and titania been involved in the past with theseus and hippolyta

In this scene, we find out that Oberon and Titania, King
and Queen of the fairies, have been romantically involved with Theseus, Duke of Athens,
and his fiancee, Hippolyta.

We are told that Oberon was
having an affair with Hippolyta.  Titania scolds him for it in this scene.  When she
scolds him, Theseus responds in kind.  He tells Titania that she should not be talking
about his affair because she was having her own affair with
Theseus.

So it seems that the fairies have managed somehow
to end up having love affairs with the human beings.