Perhaps Timon's only real friend, Flavius is also his steward, or his head servant: he runs Timon's household and is in charge of Timon's money. We can tell the other servants respect Flavius and follow his lead; we also know that he and Timon have a good thing goin'. Flavius cares a lot about Timon and doesn't want all of his friends to keep using him.
Once Timon heads off to the woods, his servants are left stranded: they no longer have anywhere to live or work. Flavius tells all the servants they are now poor, which means that they have shared in the ruin of Timon's household. If Timon's lost all his money, then he's got nothing left to take care of his servants with.
You might think that Flavius would be annoyed with Timon for 1) essentially leaving him on the streets and 2) not listening to him about his money troubles in the first place. But Flavius doesn't let that stop him: he goes to the woods and hunts Timon down, pleading with him: "T' accept my grief, and whilst this poor wealth lasts" (4.3.491).
Flavius seems to genuinely care for his master, and he wants to comfort him. He can't offer Timon money, seeing as Timon has already spent it all, but he can offer support. Even Timon is taken aback by this. He never thought of Flavius as a friend (why not?), but it turns out his steward was his only real friend all along. He's the only one who doesn't want something from Timon in return.
Flavius's kindness and concern almost make Timon believe in humanity again—but hold up, because we said almost. Sadly, Flavius can't get through to Timon. Why is that? Is Timon just too cold toward men at that point? Or does Timon just have a hard time recognizing servants and other people of low social status as friend material? Does Timon himself have a hard time recognizing friendship when it isn't backed up by moolah?
Maybe it's a mixture of both, but we have to point out that while Timon is raging about how awful all people are, he's got Flavius and other faithful servants sitting right in front of him proving him wrong. What gives, Timon?
Okay, okay: Flavius is a good guy... but is he partly to blame for Timon's troubles? Sure, Flavius is genuine and kind, but that doesn't mean he didn't have a hand in Timon's downfall. We see him try to speak to Timon about his money troubles (1.2), and we see him even say to Timon: "[Y]ou would not hear me, at many leisures I proposed" (2.2.132-133). Okay, we get it: Flavius tried a bunch of times to tell Timon about his money woes and Timon just didn't listen.
Is that any excuse? Maybe it was difficult for Flavius to bring up these troubles with Timon. We can also totally understand that as Timon's servant, Flavius didn't want to be too forthcoming with his master. On top of that, Flavius probably doesn't want to embarrass Timon in front of all of his friends.
But we wonder whether Flavius isn't just a little to blame. After all, he was the one in charge of Timon's checkbook. He was the one who was handing out the cash and jewels for Timon. He should have been on top of it, right? Timon might not have listened, but there's certainly a lot of blame to go around.
Flavius doesn't think so. Check out what he says when Timon runs out of cash:
Undone by goodness! Strange, unusual blood,
When man's worst sin is, he does too much good.
Who, then, dares to be half so kind again?
For bounty, that makes gods, does still mar men. (4.2.38-41)
Hmm… we can see how Flavius would get the idea that Timon was too good and too kind with some pretty greedy people: that's true. But was Timon also a little too trusting of his accountant Flavius? Should he have kept better tabs on how much money Flavius saved for a rainy day? Why didn't he?
Now, it's also possible—even likely—that Timon wouldn't have listened to Flavius no matter what Flavius told him, so we're not going to point too many fingers, but maybe one thing Flavius learns by the end of the play is that if you want to be someone's faithful friend, sometimes you have to stop enabling them and start telling it like it is.