Your whole (unfortunate) situation has brought an interesting thought to mind. Throughout high school it was pretty common for my friend group to share our work with each other (we were a bunch of nerds). Whether it was just notes to help each other out or actual assignments that we wanted someone else to proof read for us. We trusted each other a lot, and we luckily never had any issues with plagiarism.
It was only when I started uni this year and did a compulsory academic integrity unit that I found out that some of the sharing we did could have fallen under ‘collusion.’ I don’t know if it’s the same universally, but our uni says to never share work related to individual assignments, or we could get pulled up for collusion. Also, if you are in a testing hall, it is your responsibility to keep your work covered. If someone cheats off you, you will both be penalised.
I found it interesting that I had never heard the term ‘collusion’ mentioned at school. It makes sense, because if they do find duplicate work, it would be hard to fairly evaluate who copied who.
