It sounds like you are on the right track. Be patient and encouraging of her flirting with other men. I would suggest affirmative behavior on your part. For instance, whenever you see her flirt with another man give her lots of oral sex as soon as you get home. Be direct as possible as soon as you get in the door. Really go at it and make sure that she cums, more than once. BUT do NOT have intercourse with her. Instead you should jerk off and cum on her. I think cumming on her feet would be best (shows subservience), then clean her. It is of the UPMOST IMPORTANCE that you leave her hungry for cock - no toys inserted either. If she wants more sex, keep giving her oral sex until she can't take any more. Cuddle and be loving afterwards, reaffirming your love for her.
By doing this you will build the connection in her mind that when she openly flirts with other men you become obsessed with orally pleasing her. So she will begin to attach her orgasms to flirting with
other men, very important! But by not giving her cock (or toys), you leave her pussy yearning to be filled. And believe me, the more that you leave her pussy yearning the sooner she will need a throbbing cock and eventually she will be tempted beyond her inhibitions.
It is important that your wife be as comfortable as possible with the other man, and I think it best to give her as much latitude as possible in
her choice of a lover. Let
her take control when it comes to which man she might give in to. Perhaps you could have a dinner party with her friend's husband and all take too much wine. Of course you don't want them to drive home, so suggest that they could spend the night. If the chemistry is just right . . .
There are several upsides to this possibility. First, he is already flirting with your wife and keeping it from his wife, so that is a good sign. Second, since he is married he probably won't become obtrusively obsessive outside of the bedroom, which is a good thing. Third, since his wife is a friend of your wife and knows you your wife's lovers wife probably won't be suspicious of her husband spending time at your house. Fourth, and not least, since he is married (and presumably has been faithful to his wife until now) it could reduce the likelihood of STD's (I know - no one wants to think about it but we
ALL MUST) leading to the possibility to eventually allowing him bare back with a relative sense of safety.