One of the psalms tells us all how to avoid cynicism and repent of it. The keys to breaking a habit of cynicism are humility and gratitude towards God.
Those who have grateful hearts and those who do not dwell on the faults of others, only concentrating on repenting of their own faults, will not fall into cynicism.
from Psalm 115Douay-Rheims
10 I have believed, therefore have I spoken; but I have been humbled exceedingly.
11 I said in my excess: Every man is a liar.
12 What shall I render to the Lord, for all the things he hath rendered unto me?
13 I will take the chalice of salvation; and I will call upon the name of the Lord.
14 I will pay my vows to the Lord before all his people:
15 Precious in the sight of the Lord is the death of his saints.
16 O Lord, for I am thy servant: I am thy servant, and the son of thy handmaid. Thou hast broken my bonds:
17 I will sacrifice to thee the sacrifice of praise, and I will call upon the name of the Lord.
18 I will pay my vows to the Lord in the sight of all his people:
19 In the courts of the house of the Lord, in the midst of thee, O Jerusalem.