I was going to reply to your post but see it's been taken down. I feel compelled to reach out to you because I walked in your shoes just a few short months ago. Trust what all the women are telling you here -- "outing" him to his wife will not accomplish anything other than more heartache, probably for her and most certainly for you.
If she's been with him that long, she most likely knows or at least suspects he's not such a great guy, with or without solid "proof." She has her reasons for being with him if she knows and if she doesn't know, you telling her probably won't make her leave him. N/P are sooo good at manipulating the truth -- he'll have her spinning and begging him to take her back in no time if she confronts him and/or kicks him out.
Let time sort out that mess. They're not in an enviable marriage to say the least and I know you want him to hurt but he won't, not really, no matter what you do. It's so tough to feel so completely impotent in a situation and want to rage against the N who so completely devastated you. But your best revenge is to stay NC and focus on making your life better, for you and your dear little boy. The sooner you can educate yourself on exactly WHAT you were dealing with (not WHO because seriously, they're not exactly human), the sooner you'll begin to heal and be able to turn more attention on yourself, which is what matters most in the end.
Please stick around here and learn all that you can. If you want to PM me, I'd be glad to talk with you more and share my experiences with you.
Take good care of yourself...you deserve it. And you deserve a happy, fulfilled, narc-free life!