Never mix friendship with money.
I had a very close group of 6 secondary schoolmates, so close that we would wait for one another at the bus terminal before going to school. We also tried to meet up and return home together as we stayed near. This went on for almost 6 years, with soccer every Sunday morning, outings during the holidays.
Then, they started to play poker, betting on football and that's where all the borrowing and lending starts. Now, all of them are enemies with one another. Sigh!