If you do want to go no contact, then makeit clear you will tell his wife if he turns up on your doorstep. Do you know her email address? If I was you, I'd now, calmly, write an email to her explaining your affair, the history, the length of relationship - no emotion or anger, just details. save it in your drafts without her email address in it (to avoid accidentally sending it). If he does turnup after being told to stay away, put in her address and send to her.
That way you aren't writing it when angry/emotional - but that will end it one way or another. Even if he convinces her it's all crap, he might just be angry enough at you to not want anything else to do with you - so the relationship will end. Or his wife will throw him out - but then your relationship won't be an affair anymore, and I dont think you really will enjoy the relationship if it's dull day to day not snatched moments of excitment, so it'll end again shortly afterwards.
However, do you really want to end this situation? Because for over 10 years you haven't actually done that. When he left his wife and returned to her, you didn't then try to get him to leave again once he was well, you encouraged the situtation to continue.
I know several woman who've been OWs and I don't think it's not wanting to 'do that to her' or reluctance to be seen as 'vindictive' that's stopping you telling his wife about the affair - I think it's because it will give a finality that's out of your control to it. Right now, he wants you, he wants to keep the relationship going - you are ending it, you are blocking him, you are certain he's going to come running to beg you to take him back. Can your ego cope with the idea that you might do something that annoys him so much that he decides he doesn't actually want you anymore? Is what's stopping you properly ending it because you don't want to feel like he's fine without you? Right now, the drama is still there, this big ending of the love affair. But if you tell his wife, the drama will continue, but suddenly you won't be in the centre of it anymore. You'll be cut out and single. Do you really want that?