What just hit me? When did narcissism become contangious?

Answer: 

Hi Goldie
HELP! How does the victim of the Narc become a Narc themselves? When did I become the victim of the victim? My story is very small compared to others on this site, but it's a very confusing situation.
My friend became involved with a textbook pathological Narc 3 years ago & she has certainly taken him on a massive roller coaster ride, all the usual stuff. They broke up 1.5 years ago, but she wont let him go & unfortunately for him, he's hooked & keeps going back. Throughout this time I've helped (unfortunately I'm a pathological empath) him as much as possible, read, researched, taken short course on personality disorders to help understand, listened, plotted & supported (I'm the only person in his life that knows the whole truth), but a few months ago whilst he was temporary in NC land, I noticed that he was beginning to display some less than healthy Narc traits himself & aiming these towards me. At first I just ignored it, then it got worse, so I pointed it out to him & over the last 6 weeks it's escalated (a lot of fights). It's now an unbearable battle of being devalued, lied to & abused (I do own, some I asked for) & used. And yes, one of the lies, SHE'S BACK (right on schedule, you could set a clock by this girl) with a vengence. We had a fight the other day where he said terrible things & now he's in contact lockdown. I dont want to lose my friend. How do I help him without being the victim of the victim. Is it possible for the victim to become narcissistic themselves & can somebody help me understand how with all the knowledge he has at hand, how you could go back to that situation. Thank you! :/