Is OTHER wrong in the post ? POST : Throwaway, because reasons. Also, mobile. Apologies if needed. 

Situation is complicated, but I'll try to be as to the point as I can. Buddy of mine (let's call him Arthur) has been dating this girl (let's call her Carol) for a few years now, sorta on and off as they have their ups and downs. One big down they have is that Arthur tends to keep a lot of secrets from Carol. 

My usual policy is to not interfere in others' relationships, so I don't usually ask to meet who friends are dating (makes it easier to not get into sticky situations) and even when I do, I don't try to befriend them, or interact with them without friends around. Now, you might call that a lot of negative things, and I will likely agree with you. I am not here to win nice guy, or 'nice guy', awards. 

Problem for me started when Arthur asked another buddy of mine (we'll call him Roy) and I to help him out. Carol had wanted to try playing an MMORPG and had asked Arthur to join her and her friends in doing so. He wasn't a big fan of MMOs, and knew that Roy and I had been looking for a new MMO to occupy our free time. So after a bit of begging on Arthur's part, and Carol herself talking to us excitedly about the game, Roy and I agreed. 

If any of you don't know, playing an MMO as a small guild sorta requires members to interact with each other pretty regularly. So after a few months of it, I got to know Carol and her friends and them me. 

It was around this time that Arthur and Carol started to have one of their down periods in their relationship. Carol had found out that Arthur had lied to her about going on a group lunch meeting just to meet another girl he apparently had a thing for before. When she confronted me about the lunch meeting, I (at this point, was unaware of any issues between them regarding this girl) confirmed details she asked about.

Arthur is understandably pissed at me for "blabbing", while Carol is pissed at him for lying to her when she confronted him before revealing I had confirmed the details. 

Since I'm friends with her friends, they told me I did the right thing by telling her. But mutual friends of mine and Arthur's tell me I'm a traitor for doing so. I tried to talk to Arthur to try to tell him to just come clean with her, but he has ignored all my messages.

So, after that mouthful... AITA here? 