Fit is hiding something.
Pac isn't stupid. He's known this from day one. He's observant, much more observant than people generally seem to realize. (In fact, the only one that had ever seemed to catch on was Fit—and Mike, of course, but he's known that for years.)
He doesn't know what it is. All he knows is that there is something about Fit that is a secret. This isn't a surprise, really: the man is very private. He holds his cards close to his chest; it's what he's used to. And Pac would never ask him to change his habits like that—and certainly not for him.
But he's noticed the way Fit tenses every time someone mentions leaving the island. The way he tightens his jaw when his vacation is brought up. The way he shuts down conversations about 2b2t as fast as possible. Something is off.
Fit doesn't bring it up. Pac doesn't push. It's not his business. It's up to Fit whether or not he wants to share that information. And no one asks them any questions about it, so it's not important, anyway.
So when Mike returns all...wrong, spewing doubt from every pore, Pac...hesitates. Because on one hand, this is a man he's known for years. He has trusted Mike's instincts at every turn, the same way Mike has trusted him. He trusted Mike long before the horrors of the island had come for them both. On one hand, this is the man he would lay down his life for without a second thought—and he nearly has on more than one occasion.
But on the other hand, the thing is there is at least some validity to what Mike is saying. Fit is hiding things from them. And Pac knows this! Has known it for, like, months, at this point!
But he also knows Fit. He knows (a bit) how hard Fit worked to help Mike get him back. He knows how Fit was there for him when Mike vanished, and then again when Richas disappeared. He knows that Fit has been carefully pushing him the whole time not to forget about Mike, always keeping an eye out for any possible clues.
If Fit knew where Mike was, he would have told him.
And Mike is acting odd. They've been friends for over a decade; Pac knows the other man inside and out, and never once has he ever seen him act like this.
Mike is frustrated. He can see it in the way he glares at Fit when the larger man hands over his communicator to show the chat logs. He can see it in the way he avoids talking to other people as much as he can. He can hear it in the way Mike lashes out once they're alone, arguing about Fit's untrustworthiness. He thinks Pac should believe him. (And why shouldn't he?)
Fit is worried. He can see it in the way he hasn't taken his eyes off of Mike since the moment they found him. He can see it in the way Fit walks behind the duo, hand swinging very close to his scythe handle. He can hear it in the way Fit lowers his voice when he pulls Pac aside to talk, concern flooding his tone. He thinks something is wrong with Mike. (And it definitely is.)
Pac is torn between the two. Because Fit is correct; Mike is not okay, anyone with eyes can see it. But Pac has been away from Mike for so long—longer than they have ever been apart before—and he has been through a lot since the last time they talked.
He knows he needs Mike.
And so he reaches an uneasy conclusion: he has to believe both. Because the evidence clearly points to Fit's conclusion, that Mike is clearly not okay. And Mike may not be okay. But he's right. And Pac is simply too afraid of losing another person to confront the situation.