There is no crossing him in’s humor;
Else I should tell him well, i’ faith I should;
When all’s spent, he’d be crossed then, an he could.
’Tis pity bounty had not eyes behind,
That man might ne’er be wretched for his mind.
(1.2.157–61)

Flavius says these words to himself immediately after Timon has asked him to bring out the “casket” containing various treasures, which he’d like to dole out as gifts. The anxious steward compliantly agrees, but then privately expresses the anxiety he’s felt in trying to explain Timon’s dire financial situation. He hasn’t been able to find a time to tell Timon, since he’s always in such good humor. Yet he also anticipates that “when all’s spent,” Timon’s good nature will undoubtedly sour. The concern Flavius has here is partly about his own difficult position, but it’s also clear that he is genuinely concerned about his master.

If money were as certain as your waiting,
’Twere sure enough.
Why then preferred you not your sums and bills
When your false masters eat of my lord’s meat?
Then they could smile, and fawn upon his debts
And take down th’ int’rest into their glutt’nous maws.
You do yourselves but wrong to stir me up;
Let me pass quietly.
Believe’t, my lord and I have made an end;
I have no more to reckon, he to spend.
(3.4.47–56) 

In act 3, scene 4, the servants of Timon’s creditors gather at the estate with their bills in hand, waiting for Timon to appear so they can call his debts due. Frustrated by this pressure, Flavius goes before the creditors and confronts them with these lines. Defending his master, he calls out the hypocrisy of Timon’s creditors, who show themselves to be “false” when they send him “sums and bills” to collect money even as they “eat of my lord’s meat.” Flavius also gestures to the cruelty involved in the practice of usury. He imagines lenders lining up with “their glutt’nous maws,” ready to devour the profits they’ll make from the interest on Timon’s debt. Profoundly disgusted on his master’s behalf, Flavius concludes by announcing that there is no money left to pay any debts.

O you gods!
Is yond despised and ruinous man my lord?
Full of decay and flailing? O, monument
And wonder of good deeds evilly bestowed!
What an alteration of honor has desp’rate want made!
What viler thing upon the earth than friends,
Who can bring noblest minds to basest ends!
. . .
Has caught me in his eye; I will present
My honest grief unto him, and as my lord
Still serve him with my life. My dearest master!
(4.3.456–62, 67–69)

Flavius speaks these lines to himself when he first spots his former master near his cave in the woods. He has come with the intention of continuing to serve Timon, but upon first seeing him, Flavius is shocked at the man’s changed appearance. The sight of “despised and ruinous” Timon “full of decay and flailing” moves him profoundly and occasions a curse against false friends. When Timon catches sight of him, Flavius pulls himself together and reaffirms his intention to rejoin his master and “serve him with my life.” As the scene continues and Timon is forced to reckon with Flavius’s “honest grief,” his misanthropy will soften enough for him to proclaim Flavius the world’s “singly honest man” (4.3.521).