Sure. I guess it's just part of life. Some friends stay dear forever and some just drift away. It's a shame but it happens I'm sorry to say.
Worse than sour milk with this one:
Hmm---well when my best man and my first wife had an affair, I will admit my attitude toward both of them changed somewhat.
Incidentally, they are both dead now---and aside from reading both obituaries with considerable satisfaction (thanks, Mark Twain), I was not directly involved with their passing.
I've had a few go bad for various reasons. It's sad when that happens.
I can't think of any that soured. I have always been one of those people who have always had friends that I have disagreed with in certain areas. That is what makes life interesting. I have had plenty that we have drifted apart, but that is just life. In the last few years, now that we are getting older and have more time for ourselves, I have reconnected with quite a few.
None have really "soured", but a few have slipped to the back burner due to distance and schedules.
Only one that soured and that was because she became very demanding, calling 5 or 6 times a day then she did something that was illegal and not moral. We had been friends for 20 years but that was the end of our friendship, I've never seen her since and I have to say don't miss her.