If there's any point in working out the delicate shades of blame then sure, the OW or OM can be less to blame. Or maybe can be to blame for foolishness and naivety and bad judgment rather than malice, and for helping another to lie rather than being a liar.
There is one thing though, and that is: how could you ever have thought that his behaviour was good for his children? Maybe you never met them, and maybe all's fair among adults, but we all have an obligation to care about what we do that harms children. But it is beside the point isn't it? You got played, by him and by yourself, into believing what suited you when it was obviously just a clichéd bit of nonsense. The best thing for you is to disappear from that family's world altogether. That's best for you and best for him. Best for his wife and kids too. There isn't even anything for you to chalk up to experience, because you already knew that affairs, cheating, destroying homes, and lying were wrong. Everyone knows that. So there is nothing much to look back on and think about. Yes, if it makes you feel better, he is far, far more to blame. He is also going to have far, far more to live with from all this... if he does give a rat's about his kids, at least. You can put it behind you and invest some time into someone who is not a definite liar right out of the box. On the upside it's guaranteed that almost any random human being is a better catch than he was. You can't do worse unless you start trawling prisons.
Maybe it is okay, maybe it will be okay.
BS, d-day Feb 2017, 16 mth affair.