Why many relationships fail so easily

Months ago I had a girlfriend. She was more a friend than a girlfriend and there was not really a relationship to speak of. When I had time, I came for a visit and that was about it. Then severals months ago (last year sometime) she decided suddenly to terminate the friendship. I wiped all the contact details that I had after that since terminate means final. At that point in time I could not make any sense about the "reasoning" why that got terminated and left it at that.

Today I get a message saying that I should come for dinner even though I am now on her already quite big ex-friends list. She talks about me having been a good friend. Recently I met another woman and several weeks ago we went once for coffee and once to watch a movie together. Today the girlfriend from so long ago who terminated the friendship now suddenly says I cheated on her. How this is possible I have no idea since there have been at least four months between her and the person that I have recently met.

The above situation is exactly why I do not really want people around me who backstab me with accusations and expect me to mindread and always say the correct thing. I have had a total of two grilfriends in my life and at this rate that is two too many.