You're not a gaslighter just because you didn't want to have your friend find out about you buying SN. You didn't want him to get upset, take you to the hospital and take the SN, or beg you not to do it. You're probably afraid and sad and scared. Most people would lie like you did, I would.
I know some people who I can't talk about my suicidal ideation with because some people don't know how to deal with it without flipping out. However I do want to say that for your own sake you should talk to your friends about how you've been feeling if you think you can trust them. Cause I think having a good friend to talk to can mean the world when life seems meaningless and like no one cares.
I guess to answer your question my greatest defect is probably.. everything?