I don't even know what they're officially called. Heidegger's Public Safety Force or Public Safety Maintenance, something like that - the Shinra army.
Look, does this not sound creepy at all to you?
Hmmm, I wonder where you might be.Wait, let me guess...You're hanging out with that Aerith girl again,aren't you?I bet you're wondering how I got that information.See, I know everything about you,even if you never tell me anything.In other words, it's no use keeping secrets from me,because I know how to get information.So talk to me, Zack. You can tell me anything.Tell me about all the things that are wearing you down.
So Zack is doing his best to keep his life a secret from this unbearably nosy 2nd Kunsel, who just won't take No for an answer.
Kunsel's like the Johnny to Zack's Cloud.
Kunsel: "Zack, bro, just talk to me man, you know you can tell me anything!"
Zack: "I heard you moved on my girl while I was out of town. And don't call me bro."
Yes. Kunsel goes down to 'check on' Aerith while Zack's away, only to find the Turks are already keeping an eye on her. Zack didn't ask him to do 'check on' Aerith and never shared any information about Aerith with Kunsel. Kunsel tried to help Aerith with the broken flower wagon and Aerith told him to sling his hook.
Creepy.
As to Kunsel being friends with Cloud... I was under the impression that Cloud didn't have any friends in the Shinra military or in SOLDIER, aside from Zack who was kind to him because Zack was kind and matey with everyone. I don't want to get into another discussion about whether or not Zack and Cloud were close friends before they went to Nibelheim. I think it's pretty clear that SE have characterised Cloud as a loner who didn't have close friends. Maybe Zack was the exception because Zack could break through anyone's defenses. But I'm not on board for the suggestion that Cloud enjoyed a normal, active social life when he was training in the Shinra military, or that he regularly hung out with 2nd Class SOLDIERS.