The Blinding Knife (Lightbringer #2) by Brent Weeks

Gavin Guile is dying.

He’d thought he had five years left—now he has less than one. With fifty thousand refugees, a bastard son, and an ex-fiancée who may have learned his darkest secret, Gavin has problems on every side. All magic in the world is running wild and threatens to destroy the Seven Satrapies.

Worst of all, the old gods are being reborn, and their army of color wights is unstoppable. The only salvation may be the brother whose freedom and life Gavin stole sixteen years ago.