Well before I knew what was going on, I used to say my exes and I were attracted by our 'sadness'.
With X1, it was a shared desire to rise above our small-town backgrounds. To be fair to both of us, what we did was an achievement. People in his home town (where our relationship started) were quite vicious about our ambition, saying we'd be back with tails between our legs. I was the one to drive the changes: it would have been easier and less painful to do it alone, for myself only, but he was fully on board. Once we started to see results, we both enjoyed the trappings of a fairly glamorous life. This life was inherently narcissistic - we were welcome to jump the queue at clubs that had 'beauty bouncers', for example - so his narcissism didn't register as unusual to me (though it did to some of my glamorous friends). Where I was being 'filled' by having hundreds of sparkly, affectionate friends, his need was more insistent: adulation. Being told how fabulous you were and hugged by hordes wasn't enough; he had to be at the centre, holding court. Over time, people told me he was out of kilter but I didn't hear them right. The 'sadness' we shared held me in the relationship so I didn't see that I was only an accessory to him. The glamorous friends; the automatic entry; the memberships and invitations ... they were all mine. He called them ours and I never questioned that.
He said he made my success - er, because he influenced my choice of clothes and music?! He sometimes quoted the Human League lyric: "Don't forget it's me who put you where you are now. And I can put you back down too." That places us squarely in the 80s, doesn't it 
By the end, I saw him as a hopeless case. A one-off, designer case made of the finest stuff, with nice things rattling around the hollow interior! I still felt the sadness, though, and that made me too soft on him when we split - even after he strangled me, god help me. And that's how I lost everything the first time.
Narc flatmate and I were drawn together by cynicism. We were both good with dark humour although I never found any roots to her pain. She, too, was a crowd-gatherer and friend-stealer, 'filling' her self with drugs and other people's husbands; making herself feel better by making me feel worse. After five years of increasingly overt hostility, I moved in with another Narc just to get away from her.
I think I married X2 to get away from the second Narc flatmate. X2 was the opposite of the others - quiet, sullen, unassuming. I was feeling very, very cynical at the time and my (humorously) negative outlook found expression in his darkness. You know all those pulp romances with a brooding hero? Like that 
I felt we had an understanding that surpasses words. Which is just as well, as he was absolutely shite with words. I thought he had some sort of affliction which, once I learned about Asperger's, fitted that description. I still think he has, but there's more to him than that. He is a fraud, a thief, a bully, sexist and is horrible to people who cross him. Really horrible. He bears grudges. My romantic side - the 'sadness' - felt we were both outcasts so he played on that. Of course, I wasn't really an outcast. I brought experience (older than him), knowledge, contacts, ambition, prettiness and money to his life. He brought me good sex and screaming insecurity. The insecurity made me feel more bonded, as if I needed him, where all logic said he needed me. But, then, I 'needed to be needed'. The marriage didn't last long and he played a long, cruel game to make sure I got nothing for all my contributions.
So - after yet another long blurt about my life - I got around to identifying this 'hole' and set about filling it properly, with the long and difficult processes of inner child work. My therapists have been extremely helpful - I wish I still had one - but, you know what? Mumsnet has been a truer guide to what the problem is and how to stay (roughly) on track with recovery. If the sociopaths who shaped me have taught me anything, it's that this 'hole', my sadness, cannot be filled with anything or anyone external to myself. I have felt as if I've needed to tear down my own identity, like a house that was built on quicksand, and start again from scratch. I'm only in the very early stages of seeing which bits of the old 'house' might be worth reclaiming and incorporating into the new, more stable structure. Just writing that makes me feel sad.
I believe it could be done more quickly with fuller recognition and appropriate guidance, which is why I'm labouring the point a bit. Not all victims of sociopaths were trained to the job by sociopathic parents, but very many were. For us, recovery - and immunisation - begins in Stately Homes territory. It's a pain in the arse ... but at least we're capable of it! Sociopaths aren't. And there's the difference: the understanding of what it is to be fully human, with enough self-insight to want it instead of mimicking it.