Is it normal a mans spouse to share her fantasies with a complete stranger?

You seem to have already made your mind up with multiple answers suggesting it isn't normal or that she is cheating. Why are you coming on here yourself and asking complete strangers? Could it be you want to feel validated in your own belief? Hear from like minded people who may understand what you're going through or feeling? I am not saying what they did was right I am just asking you to consider the idea as Gspyder suggests... Why don't you talk to her about it? If she is doing all this writing have you ever jumped in and wrote her a naughty letter? I don't know about others but I can tell you that reading intimate words is like porn to me except my mind can go into more detail...

It is probably easier sharing fantasies anonymously. When it is with your spouse people worry about if they will be seen differently, if the spouce will think "the usual" isn't satisfying them anymore, or maybe they think their is no point because the spouse isn't into whatever fantasy.

It's really nice to be able to push past that discomfort though and be open and able to help eachother explore your own individual fantasies and fetishes.

Desires and fetishes are a funny thing. They are so personal and they hold a threat of judgement should they ever get out. Even if said thread does not actually exist, it feels strongest with people you have to face in everyday life.
Desires can be a funny thing because, while you may be able to imagine that moment you get out of your comfort zone and share these intimate details with someone you are close to, when the moment comes it may be all too easy to clam up and misdirect towards more "boring" routes.
Does she know your desires? If you two are still generally happy together then I would bet that she DOES want you to know her desires...she just has a hard time getting over that knot in her stomach whenever she approaches that barrier.

So just to be clear, she stops your attempts to fulfill her fantasies? I'm not sure how I feel about this part.

But even so, you surely must have some of your own. As much as a girl loves being pampered she also need to know how deep your rabbit hole goes as well. It can't be ALL about her...especially when that part of her may be her darkest secret. You know, or maybe she hasn't even explored her own dirty thoughts enough to know herself.

Let us say, for instance (and a very dramatic instance to make my point), that she has a pee fetish. How crazy this must be! Surely she must take this to the grave! The mere thought of sharing it is enough to give a woman hives.

Deepthought33; Since have always been open that my desire is for her happiness and whatever she wants and every time she has expressed a desire I have fulfilled it or attempted it with her stopping it from happening. Would that differentiate your opinion of the situation?

Actually in the past I have actually wrote her naughty letters and have even engaged in sexual chat with her. Sometimes via a chat session when we were both in the same room together. That's why I don't understand why she would reach other to someone else, when I have obviously shown in the past that I am open to whatever she desires. My biggest issue is that IMO she doesn't want to discuss her wants or desires with me and perhaps that is due to she is bored with our relationship and no looking for something else or wanting to move on. If she was simply looking for like minded people who may understand what her wants and desires are; I would have hoped she would have approached me and us pursue it together, rather than have been blind sided by her actions. I still love her with all my heart; however, it has placed me in a situation that creates distrust as well as questioning what she really wants.