I'm going to use my dad's depression as the theme for a college application essay
How do you plan to frame this subject?
My essay is about coming out of suicide and depression.
While it's great that your dad's voice can be heard in your essay, you need to be very respectful of that. He is not an object or property to write exotically about, nor can you romanticize his struggles. His issues need to be written with tact and objectivity so it's non-offensive.
Well, I'm just writing about my dad's depression.
Have you asked him about it? It can be a very hard issue to talk about. People might not like their dirty laundry being shown to the world. It would be better to communicate with him than risk hurting him.