Saying no to the friend who always copies your homework isn’t mean. It’s showing them where you end.

A friendship with no edges turns into a service. Once somebody has learned your answer is always yes, they stop asking and start assuming, and the resentment building in you will do more damage than one refusal ever would. A limit is information rather than an attack.

Say it the next time, not the time after: not tonight, but you can go over it together at lunch tomorrow. Offer the help you actually want to give instead of the help being requested. If the friendship cannot survive a single no, that is worth finding out now.