It is hard for me to evaluate without knowing the entire history. The reason I asked about the mutual friends is because I think something similar happened to me.
In this story, let's call two guys Beavis and Butthead. Beavis and Butthead are close friends. Beavis lives in the East Bay and Butthead lives in Sacramento. I hang out with just Beavis more because of proximity. But my relationship is about the same with both, good friends but not best friends. Every other weekend Butthead drove to the East Bay to hang out with Beavis. Sometimes Beavis invited me to hang out with them. But a lot of the times Beavis did not invite me, I guess it wasn't convenient or they were doing something they didn't think I was interested in. I always found out what they did later from Social media. But it was not a big deal to me, it is understandable.
At some point Beavis stopped responding to my messages. I thought something might be wrong, so I contacted Butthead even though I normally did not talk to him directly as much. Butthead ignored me as well. Later I found out that Beavis and Butthead had a fall out and I guess they didn't want me know either of their whereabouts in case I am still in contact with the other.