Noun
dark night of the soul
(Catholicism) a period of time in which a holy person (someone believed to be potentially on their way to sainthood) experiences a seeming withdrawal of God's previously-felt presence in their lives, and undergoes stark spiritual attacks. This period of time is seen (by Catholics) to be a period in which God is calling the holy person to rid themselves of any remaining vestiges of self-pride and vanity that they may have.
Your dear friend ought to take heart. From what you have told me, it is quite likely that they are going through a dark night of the soul.
Synonym: dark night
In a real dark night of the soul it is always three o'clock in the morning, day after day. F. Scott Fitzgerald
If I believe in anything, it is in the dark night of the soul. Awe is my religion, and mystery is its church. Charles Simic
A lost election can have the jolt of a drop through the gallows door, leading to a dark night of the soul in which the future presses down like a cloud that will never lift. James Wolcott
The dark night of the soul is a journey into light, a journey from your darkness into the strength and hidden resources of your soul. Caroline Myss
Being human is a complicated gig. So give that ol' dark night of the soul a hug. Howl the eternal yes! Friedrich Nietzsche