Bit of a back story to this one: My (now ex) GF and I went to different universities, so we had very different circle of friends. There was a girl (we'll call her Mina) within my friend group that GF didn't like. It was mainly cause she believed that I had a crush on Mina, and that Mina and I had a lot of classes together that we tended to study together. Other friends would call her my "Work Wife", which in turn made my GF dislike her more. Similarly, there was a guy (call him Rob) in my GFs circle of friends that I didn't like. So when I graduated from university, we both agreed to not see Rob and Mina respectively. 

Fast forward to a few months ago. I still had a bunch of friends from university that I hang out with regularly, mostly guys, who I've introduced my GF to. One of them, Jake, had some difficulty finding a girl, so another guy, Mike wanted to try to set him up with a girl. We had a discussion on who to try to set Jake up with, and since Mike had recently been in contact with Mina, he suggested her. We were gonna invite Mina to meet-up with us for lunch with the intention of trying to get Jake and her to talk to each other. Knowing my gf wouldn't like that, I asked the guys to promise to not mention it to her, especially since a few of us were gonna meet up with her after the lunch for our usual hangout.

It was also at this point that my GFs friends had her start playing an MMO. She had asked me to play with her too, but since MMOs were not my thing, she asked others in my group of friends. Two of whom agreed, call them Ryan and Peter. 

Fast forward again now to a few weeks ago. My GF and I have had some disagreements recently, and in our arguments, she had revealed that she knew about me meeting up with Mina for the lunch thing (Jake and her didn't work out incidentally). I immediately knew it was Peter who had informed her as she had grown fond of him during their time playing together. I had asked her to not talk to him anymore before (adding it to the ban on Rob as well) which she had refused to do so. Not to go into too much detail, but after many arguments with her, we both decided to break up. During the arguments tho, Peter would message me about them; she had evidently been confiding in him about our troubles, and he was trying to tell me to come clean and apologize about the lunch among other things. I didn't wanna talk to him tho as I felt that he had betrayed me and started to share my secrets with her without bothering to talk to me about it. 

After the breakup, when other friends in the group found out about it, I asked them to not speak to Peter anymore. One of them told me that that was going too far, but had agreed as well. So my question now is AITA? 