I had an old friend that I knew since high school (in the 80's). We finally had a falling out while in our 40's, for a variety of reasons. Proper phone etiquette was one of the reasons, a small one, but the one that broke the camel's back.
In college we naturally drifted apart and later lived in different states and during the Facebook explosion of the mid-00's we reconnected. He would call me from time to time and we'd always chat. Like three times a year. There was one in-person visit (his home).
Years later after he got a permanent boyfriend, he seemed to take a weird turn mentally and kept losing jobs and was home all day, so he began calling me more and more until soon it was once a week. I thought it was too much but indulged because he seemed to be going through a rough patch and we still had things to talk about. There was a little weird behavior on his part (I'm hardly perfect either), but also good laughs and shared conversation so it was fine.
If ever I wasn't there he'd leave a message asking him to call him back.
But eventually he got weirder about calling me. Soon, I stopped answering the phone on his weekly call as he talked into the machine, because he'd become a creep to talk to in the first few minutes of the conversation. He began to start every conversation with, "Why didn't you answer? Were you busy or something?" And if I didn't have a solid answer he'd get slightly incredulous. Saying, "If you don't have an excuse for picking up I assume you don't want to talk to me." Huh? Then he'd seem to get it out of his system and cheer up and it was fine. I kept ignoring the red flags.
Then things got worse...