I also know someone who goes into detail about other people's lives. She endlessly talks about people I will never meet and do not even care about. It is so boring to listen to her go on and on about other people's life-drama.
I finally had enough and told her "No offense to those you talk about, but their lives are of no interest or consequence to me. Perhaps you should reserve your comments about their lives to those who know them." At first, she was offended but that, to me, was irrelevant because I was being offended FIRST by being subjected to all of the mindless gossip and chitter chatter of strangers lives.
I did have to remind her from time to time to stop talking about those people. After time, I realized our conversations got shorter and shorter because she had nothing to say when she was not minding other people's business. I also thought that if she is blabbing everyone else's private details of their lives, she is most likely talking their ears off about my life. SO, I stopped sharing personal details of my life and just talked about my gardening, what I cooked for dinner, and other non-personal things.
As time went on, we talked less and less. I realized that some people are in your life for a reason, a season or a lifetime.