If you allow a PC to belong to a secret order, it's not really a stretch to think that the player might assume that he could, y'know, contact that order.
There ya go!
It's important, in my mind, that the DM makes the player's choices fun. Once you've said "okay!" to a dark cleric of secrets and evil, it's your job, as a DM, to present them with challenges and give them appropriate rewards. You should give them secrets to keep, dark rites to participate in, good-guys they can kill, shadows they find security in, etc., etc., etc. There should be challenges that reflect his nature: he SHOULD have to risk a town finding out about him, a wanna-be hero chasing him down, rival cultists wanting to reveal his secrets, etc. And he SHOULD have to face these down.
If you're throwing a roadblock at a character whenever he just wants to chat with some of his peers, though, you've kind of boned the character for his character choice. You've made it "not fun" to play the character, because that character experiences some special disadvantage that is in no way compensated for.
It would be similar to saying "Yes, you can be an elven sorcerer! But magic is rare and secretive!" and then making the character deal with not having a spellbook, familiar, or component pouch because "there's no way he could have attained these when magic is rare and secretive!"
Or allowing a thieving rogue who then is automatically hunted and who has wanted posters on every inn and who can't go into any town for fear of being apprehended.
You've effectively made it more difficult to play that kind of character in your setting. You've
unbalanced things, as surely as if you let a level 3 commoner adventure with level 15 paladins. While many players might not mind playing in an unbalanced party, it should hardly be expected to be the *norm.*
This assumes, reasonably, that the equipment and aid were more along the lines of "visiting town to rest and resupply" than something special and significant. Equipment and aid generally are relatively minor, assured things for a character to have, but if the setting is especially tough or gritty, I suppose they might not be, and asking for such things would be a great reward.
Basically, you shouldn't put roadblocks to any character you've accepted for their basic operation and requirements unless doing so is part of a grander scheme that the player can then thwart. Like taking away a Wizard's component pouch, it's a harsh tactic for a DM to take, one that, for many players, really hurts their ability to enjoy the character.