Activity-based friendships are not real
My friendships end because I lose interest in the activities that cultivate those friendships. I lost one friend because all she wanted to do was walk and talk and I got tired of walking through the same neighborhood week after week. Another couple of friends I lost because I wanted to go to bed earlier to work out in the morning, and they only wanted to go out late (these were friends I knew for a really long time). Another, well she was just my co-worker and I never saw her much outside of work.
I still like these people. But after turning down a few invitations, I ignored them because it felt like I was making excuses. So, now I have no friends because I don't consistently have the same interests that they seem to have.