Very similar thing happened with me and my group of friends. He broke up with his wife for a while, and when they got back together it was like something went wrong in his head. He started trying to mess with people for fun. One day he got drunk and bragged to me about how he was purposely getting closer to one of our other friends to purposely try and break him and his missus up. I noticed he was starting shit with me, so we had a falling out when I called him out on it. Then the rest of the group started actively ignoring me. I eventually got told by someone who was in an outer circle hat he was talking shit about me behind my back to everyone. Found out that he has actively tried ruining other relationships for his own sick entertainment. I'm wondering if he developed a brain tumor to start exhibiting this behaviour, whether he developed some mental illness when he got back with his wife, or if he was like that all along and I'd never noticed. I'm a lot lonlier now and miss my friends, but I refuse to go chasing them accepting the fact they see our 16 year friendship as expendable garbage.