I'm going to break my friend's trust and cause her embarrassment at school
How do you plan on doing these things?
I am going to catch a foreign exchange student cheating when she told me about that in confidence.
It is normally okay to do the right thing but it will cause you to betray your friend's trust and it will hurt them. It could also lead to the end of your friendship.
It's cool my friend said that I can date her once she goes to university.
You should do your best to not break the trust that your friend has in you. If they told you something hoping for you not to tell other people, than they would be very upset to find out that you exposed their secret to other people.