What is "Shetzef Ketzef"?
Rashi citing Menachem: It is fury. Radak - he explains b'Shetzef like b'Chari.
Rashi citing Dunash, Targum Yonasan: It is a little anger, like "b'Rega Katan Azavtich" (7). Radak - this is like verse 7; The matter is repeated in different words to strengthen it.
Malbim: I hid My face from you for a moment amidst anger and repulsion - this was a little anger compared to the Chesed of pardoning the sin.
What is "Chesed Olam"?
Rashi: It (Malbim - pardon of your sin) will last forever.
Why does this verse mention Chesed and mercy? Verse 7 mentioned only mercy!
Malbim (7): Verse 7 discusses an abandoned wife; mercy suffices for her. For a despised wife, mercy is not enough, for he is angry due to her sin. First the anger must depart via Chesed and pardon of the sin.