I've never said the n word.
Has there ever been a time when you would have?
No, not yet. I don't plan to either.
Some words can be very offensive and it is good to know that you shouldn't say offensive things to other people. You will lose friends otherwise.
I'm sure it's fine for my black friend to say it, just not me.
It's possible that your friend would forgive you for saying the word, but he would still lose respect if he heard you saying it.  Because that word has such a long history of racism, and since you have nothing to gain from using it, I would recommend that you continue to live your life without it.