Maybe just a passerby

I had a friend, let's call them A, who I used to be quite close with and played games with every day. Then I introduced A to another friend, B, and A and B became really good friends, sharing everything. One day, B got a girlfriend, but she didn't like some of us, so they started cutting ties. After that, A also suddenly cut ties completely, not replying to any messages... Thinking about it, I guess they chose a side. Even now, the relationship between A and B is like the one I had with A back then, and although A hasn't explicitly said it, they're probably with B's girlfriend now. -- Update later B is currently bothered about why A is ignoring him and might have written a long message. They haven't unfriended each other, but B might have some lingering resentment.