Zalhonan,
Welcome to Marriage Builders. Your title says that the cheating hasn't started but the body of your post says that you feel betrayed. That sounds to me to be real betrayal even if it isn't physical. It sounds as if your wife is involved in what is called an Emotional Affair or EA.
I do believe that exposure will need to happen at some point. I'd even be willing to bet that she will flatly refuse to end the relationship and be very angry and vindictive that you would even suggest it. That in and of itself will be the barometer by which I would decide how to expose and to whom. When exposure does take place, be ready for nuclear holocaust to begin. You never even knew that she could be THAT angry. You need to be prepared for that as well as have a clearly defined plan of who to expose to and have enough compiled evidence that you don't look like an idiot when she tries to spin her relationship with this guy to her family and friends. You don't need to meet the requirements of evidence to be used in court because you only need to have things that point to what is going on and not a smoking gun in her hand. You aren't trying to convict her, just make the fantasy develop a few cracks.
Though many a wayward spouse has considered this type of "friendship" to be something innocent, it is far from the truth. The fact is that you have been deeply hurt by her feelings for this other guy and her feelings for you have been damaged by them as well.
Is this guy married as well? If so, his wife might be your biggest ally and should certainly know pretty soon.
In direct answer to your direct question...Yes; I would begin Plan A at once. By the fact that you have asked that question I am assuming that you are familiar with what that means. Rest assured that it is not an easy process and will lead to loss of appetite, lack of sleep and untold stress, but in the end, it will lead to peace regardless of the outcome of the marriage.
I would suggest that you might want to move your story to the General Questions II forum under the infidelity section of this board. The amount of traffic there is much greater than it is here and there are many who are right where you are in all of this as well as many more who were not that long ago.
If you have not already done so, be sure to read the basic concepts and the Q&A columns related to infidelity. I assume you know something of the work of Dr Harley since you asked specifically about Plan A. Have you read Surviving An Affair? If not I would strongly recommend it. Many will point you toward His Needs/Her Needs and Love Busters as well, but I have found the newer book Fall In Love/Stay In Love to be a good summary of both.
You also might want to read the first few threads pinned to the top of the Just Found Out forum on infidelity. Pay close attention to Longhorn's thread and WAT's Quick Start Guide for betrayed spouses. The other posts pinned to the top will give you the abbreviations and answer a few questions a lot faster than having to ask and wait for someone to reply.
FWIW, whether this has gone to the physical level or not, it is not an appropriate relationship for a married person to be involved in and as you have said is really little more than a fantasy.
Don't worry about being confused right now in your posts. We've been there and done that many times over in this place.
Consider the move to GQII and buckle up because it does tend to get bumpy pretty quickly.
Best of luck to you, Zalhonan...
You are not alone in this. Many have gone through it before and unfortunately many more will in the future. Given the circumstances Marriage Builders is a good place to be.
Mark
