How do I introduce myself into the equation? That's THE question. Any suggestions?
I'm very curious, and maybe you've answered this, but how close of friends are you and Ron(or how close were you before this)? I ask because I want to know how open he would be to knowing that you know about the initial proposition of the affair and that'd you'd be cool with her playing with him under certain parameters. If you have a cordial conversation with him and get him on the same page, you may be able to approach it from the angle of inviting him over with the intent of him coming onto her after she's relaxed, her being surprised and a little resistant, only for Ron to have her look up or turn around and see you smiling with approval.
She may like your acceptance of and assertiveness over the situation. That you're allowing her to express herself outside the marriage, but only under the parameters you've set. That's part of the Stag/Vixen dynamic. Right now, you're headed down the cheating and/or cuck path and, considering where you posted this thread, that doesn't seem like where you want to be. I actually don't know what country you're in/from, but if you're American, you know our women generally like their husbands to be in control, even of a situation like this. She wants to feel naughty and have a sense of freedom, but also feel safe and led, especially when she's unsure. It's the paradox of the western woman.
A situation like the one above let's you have your fun and her be reminded that you're a man she respects. A man who loves her enough to let her play and who is also confident enough to know she's not going anywhere just because another has her body. I don't know if you read my post about how my wife and I crossed over to playing, but nothing was hotter to her than when I confronted the guy who was trying to lure her into an affair and put him in his place. She was wet as hell, I'm telling you!
Take control, communicate openly and trust me–you, her & Ron will have the most fun! If he doesn't want to keep playing because you're aware of the "affair", but she's now open to the lifestyle, you've just opened the dream scenario where you two now get to pick the guy(s) you play with and they know/agree to the rules from the start. She never has to cheat, feel guilty, etc.
Because make no mistake, Ron is trying to cuckold someone in your friend group(didn't someone remark in your OP that yours wasn't the first wife he approached?) When a man not only wants to fuck your wife, but talks about sharing her with his friends without your knowledge or consent, he needs to be put in his place.