Remember That You Trust Me

The loner learned his lesson. He will no longer declare I Work Alone; he has made friends and learned to trust them.

So why is he sneaking about with secrets? Aesop Amnesia?

Nah, just bad habits. One of his True Companions just has to remind him of the Power of Friendship and the The Power of Trust. Let it be known that his mistrust is hurtful. Distinguishable from Aesop Amnesia in that they do not have to learn the lesson over again; the reminder often suffices, for an explanation of secrecy if not an actual explanation.

A form of Character Development more realistic than simple Epiphany Therapy at that.

Sometimes needed when the character learns new things and tries to keep them secret. Sometimes can be dangerous, if there are good reasons for secrecy.

Examples of Remember That You Trust Me include:

Anime and Manga

In Natsume Yuujinchou, Natsume is so used to being a social pariah as a child for disclosing his somewhat creepy ability, that he's become very reluctant to talk about it to anyone—even friends who know he can see spirits and Youkai, or would still readily accept him if they knew.
A lot of this between Kotetsu and Barnaby from Tiger and Bunny; even after they get to the point where they start to trust one another, both have their reasons (with Kotetsu it's his fear of "becoming a burden" on someone while in Barnaby's case - since Kotetsu is his first and only friend and confidant - the habit of twenty years) for not sharing certain things with one another.
One Piece; at a crucial part of the Arlong Park Arc, Luffy gives Nami his hat - his most prized possession - to prove to her she can trust him.

Comic Books

In the Age of Apocalypse, Rogue frequently reminded Magneto that he had promised not to keep secrets from her.

Film

Predator 2. After Danny is killed by the title creature, Lieutenant Harrigan wants to take it down by himself.

Leona: Mike... Mike, goddamn it. This ain't your personal little war, you know. I loved Danny too.
Jerry Lambert: And you told me, lieutenant, "the only way you survive down here is because you're a team." "The door swings both ways," remember?

Literature

Dan Abnett's Gaunt's Ghosts novels:
- In His Last Command, Kolea finds Rawne and the others from the Geroen team meeting in secret, and blasts them for forgetting their Fire Forged Friendship and not trusting their commander.
- In Blood Pact, when Curth stumbles on the secret transmitter, she wonders why they kept it so secret. Hark explains that he was trying to keep it secret as possible, so they wouldn't be hurt by knowing.
In The Dresden Files, at one point, Ramirez reminds Harry that they're Fire-Forged Friends and tells him that he knows he's keeping secrets from him
In Steve Parker's Warhammer 40,000 Imperial Guard novel Gunheads, Siegler blurts out that they know Wulfe was helped by a ghost (in the Backstory), and with that out, his squad tell him that they were hurt that he didn't tell them.
In Dorothy L. Sayers' Busman's Honeymoon, Harriet tells Bunter to tell Lord Peter Wimsey that she is sitting up the night of the execution. In due course, he shows up, apologetic for having—he admits—forgotten.
Happens repeatedly in the Mistborn series, as the protagonist Vin is extremely paranoid thanks to her upbringing. Then it gets turned around a bit in the last book; Vin can't talk about her plans or else Ruin will hear, so Elend has to just trust that she'll make the right choices.

Live-Action TV

Mac Taylor from CSI: NY suffers from this frequently, most noticeably After the death of Angell and he is caught up with the solving the case. Stella actually tells him that he isn't alone.
Michael Westen of Burn Notice also sometimes needs this reminder, perhaps the most clear-cut case being in "Enemies Closer":

Nate: Jesus, bro. Dad's dead. You're not in Afghanistan anymore. I mean, when are you gonna learn there are people you can trust?

Gossip Girl: In three consecutive episodes from the third season, Chuck draws away from Blair while dealing with a serious situation, then after a gentle prod from her he remembers she's there and opens up to her.
NCIS: Subverted. Gibbs isn't willing to draw his team into a case where he's breaking the rules to protect his old CO. Tony and Kate are hurt and assume that he doesn't trust them, but Ducky explains that while Gibbs is just protecting them from the legal consequences of his actions. Then they play it straight by reminding Gibbs that they're there for him.

Web Comics

In Alien Dice Lexx has to be reminded of this, along with You Are Not Alone, every so often.
In a Schlock Mercenary arc, after the Toughs discover that their memories have been tampered with, Petey offers to help set them straight. A leery Tagon asks Sergeant Schlock (whose unique neural physiology means he's the only one with an accurate picture of what's been going on) if he remembers anything that might help him make a decision.

Schlock: I remember that Petey's our friend.

Western Animation

Teen Titans: After the first season, there's a few times Robin had to be reminded that all the Titans are his friends and want to help him.
- There are times when this trope applies to Raven as well.
In Ben 10: Alien Force, Kevin Levin can't seem to wrap his mind around the fact that Ben and Gwen trust him now that's working with them to stop an Alien Invasion, if his stealing their grandfather's RV to trade for an important message from said grandparent is anything to judge by.
In the Justice League episode "Starcrossed", Green Lantern tells the other members of the League (who are now fugitives, given the Thanagarian army's invasion - that they have to lay low, which means getting rid of the costumes and posing as civilians. The Flash is hesitant to do so, as he's not sure he can trust them enough with his identity. Batman quickly assures him he can by not only pointing out that he knows his - and Superman's - identities already, but reveals his to them right then and there.
In Harley Quinn, a Battle in the Center of the Mind (the mind in question being Batman's) Harley learns the hero's identity. Later, she assures him the secret is safe by claiming "patient-doctor confidentiality". While one might say he trusts her a little too much, she manages to abide by it.