Man there is no turning back if you take this path in your marriage.
Think it through big time!!!!
You have to seriously consider your feelings here as well.....I mean it can be labeled anyway you want....but it still comes down to she will be sleeping with another man....thats another mans cock in her mouth, inside her and touching her the way you do.
I mean if you can honestly say thats something that wouldn't bother you...hey I say "Charge!!!"
You are at a defining moment in your life right now...for your marriage...and for you as a person.