if your wife is really interested, then the key is just picking the right guy. make sure its a guy that has done it before, set ground rules ahead of time meaning since u two never did this, u dont know how it might go when its "showtime"
so that means, if the foreplay is good and this bro and ur wife are ready to get going but u're feeling tight abou it and not wnting it, the bro needs to back off. this is still between u and ur wife so if up to the point of penetration u decide u cant handle it, the bro needs to be able to understand that and walk away. the said, it also means u and ur wife better damn sure have a pretty good level of interest in doin it too, we bros arent just there to turn down like that either. sure it happens but the key is to make sure u and ur wife want this and find theright partner.
next thing is with rules and just make sure ur wife and ur expectations are on the same page and the bro too. if your wife enjoys it, how often will u want this to occur? how often would she want it vs what u want? what if your wife cant loosen up with you watching but partially enjoyed it? u willing to let her get sexed privately by the guy? if u dont like it but she likes it, is it over from there or can u handle a dont ask/dont tell deal down the road?
u gotta cover all the bases man.