It was a well described article about cheating. You pointed almost every possible reasons behind cheating. It seems you have a lot of experience of cheating 😅.
In my opinion Best friend used to do such kind of things which you faced in your case. I don't considerate has a cheat😅.

In case of your second example it's very bad happened with you. I never had such kind of experience. Maybe it's because my personality keeping me safe from that kind of cheating.
!LUV
!PIZZA