Why is it so hard to get over narcisissts?

my ex N&i brokeup 6mons ago.we were 2gether for2yrs,but he brokeup w/ me when he went on antidepressants bc he said "now that he had meds2make him happy he didnt need me"&that was it.he IMs me from time2time seeing if im dating ne1 else,tryin 2b nice, but really it seems like he just wants2kno little details of my life b4 big changes(he IMed me right b4 i left4college,right b4 i went2prom w/ another guy,who i was dating&right when he heard that i was dating som1 else)during the relationship he broke up w/ me over20times,just so that he could act as if i did something horrible wrong&so that i should feel honored if he took me back.i never cheated on him or nething,always stuck up4him&supported him.since the breakup hes gotten a fake ID, drinks every day&every night,got a DUI&a speeding ticket4going 140mph&is rumored of doing coke.i kno it sounds like the life of a sad person(gettin in SO much trouble since the breakup)yet from the outside he seems happier than ever?is it a front or wat?