1)
What is the comparison to a Nidah?
1.
Rashi: Her husband anticipates - when will she purify herself and desire to return to him?
2.
Radak: Keneses Yisrael is metaphorically called Hashem's wife. At the time of her sin, she is like a Nidah; her husband distances her, and draws her close after she becomes Tehorah. So Hashem distanced Yisrael and exiled them to lands of the nations, due to their sin. He will return them after they repent and purify themselves from their sins.
3.
Malbim: This discusses Bayis Sheni. Yisrael were Metamei the land via their ways and deeds. Hashem did not divorce them. He just separated at the time of their Tum'ah, and waited for them to purify from it, and then He will return to them.
