i have to write about a time that i've broken a promise or a time that somebody has broken a promise to me. can anybody help me think of something? it can be made up. i can think of a few things but nothing that i would be able to write a whole essay over.

Don't make it up. You have broken promises to your mom many times. You have broken promises to yourself Many more times.

In the essay, you can include more than just the event: discuss the nature of the intent to keep promises, what influenced you, what could have been done to prevent it, etc.