How long have you been seeing the therapist? Have you ever asked yourself if it’s your narcissistic side coming out when you say they’re out of their league with you? That’s not an insult, it’s a genuine question and it’s one worth asking yourself. Don’t give up therapy, because it might be one of the only things that can truly help you. As for your friend… I think you should tell them if and only if you’re truly willing to work on your problems. I mean, what’s the point of saying “I might be a jerk sometimes because I’ve been diagnosed with a narcissistic personality” and using it as an excuse for your negative behavior? On the other hand, if you are planning to work on your problems and not using it as an excuse, then yes, tell them. It will only help them hold onto the friendship if you have a bad day, because at least they might understand where you’re coming from. All in all, put excuses aside, work on yourself and be honest with your friend. Honesty is, after all, a huge part of a genuine friendship. Someone will be more inclined to help you if you let them—- and that includes your therapist. Think about it and good luck.