There's this thought that I have to write a book even though I know it would hurt my mentally-ill yet former friend.
Is there a reason why you are having a difficult time with this decision?
I don't like the idea that I hurt some people around me for no reasons.
I think that you should write the book. I know it may be hurtful, but it is not okay it to control your creative work.
I think writing it would be bad. I'd like to get rid of it, sorry.
Well you're free to do whatever you want with your work, but if this is what you really want to write then you should. If you are feeling creative and like it is something that you want to do, then you should do it.