This a post from 'Accuray'.. Basically he put it better than I tried..
Security is important to married people in general, and pushing your spouse away as she's done is really taking a big chance in terms of losing your security. People generally aren't willing to do that unless they have someplace to land, in terms of someone else to comfort them and share intimacy.
Usually when it happens quickly as you've described, your wife started out in a friendship that very very gradually crossed the line into becoming inappropriate. When she realized that she was over the line, she felt very guilty and conflicted about what she was doing. The new relationship feels *so good* that it's almost impossible to give up. Therefore, the only way to feel good about things is to convince herself that she's being righteous, and the only way to do that is to make you the villain, or the source of her discontent.
Unfortunately, when you get to this point, she resents you. If you want to save your marriage, whatever you do right now needs to be measured against a yardstick of resentment -- will your actions create more resentment, or less?
When you pursue her, she resents you because you are expecting her to reciprocate and she doesn't want to.
When you make her responsible for your feelings by being upset around her, she resents you because she doesn't want to be responsible for you.
If you shame her, she will resent you for making her feel badly.
Basically ANY form of pursuit or relationship discussion will result in resentment and push her farther away.
So what can you do?
Unfortunately, you can't begin repairing things while another man is involved, it's just impossible. All you can do is (1) not make things worse and push her away further, and (2) spend the time to work on yourself and become a husband that only a fool would leave.
This is a marathon, not a sprint, and the majority of it is simply a waiting game. The best thing you can do is give her space, and create a life for yourself. Get out and meet new people, pick up new hobbies. Be pleasant to her, treat her like a friendly co-worker. Do not share intimate details of how you're feeling, don't go out of your way to do anything for her. Don't seek her out.
If she approaches you, you can mirror, but do not escalate. i.e. if she hugs you, you can hug her back, but don't kiss her, that kind of thing. Do NOT say "I love you" for any reason. There is no need to explain how you're feeling or what you want because right now she understands how you feel and she doesn't care -- it's not about you right now.
This is a horrible, horrible thing you're facing, but you're not alone. Post often, even if it's just journaling, and read the books. Realize that you will not see any progress or improvement for quite some time. Before that can happen, things with OM need to be over, she needs to grieve the loss of that relationship, she needs to see and believe that you are acting differently than you did in the past, and that a relationship with you in the future would be different and better than your old marriage. She doesn't want to go back there, so if she thinks it will be more of the same she won't be interested.
Take the time to understand what she needs, what your issues are, and what you need to do to be the best relationship partner possible. No matter what happens with her, that will serve you well -- you'll come out of this a better person and will have better relationships going forward, and that's the silver lining in an otherwise terrible turn of events.
Accuray.
Hope this helps.
Regards, Gyn.
Cause all of the stars, Have faded away, Just try not to worry, You'll see them someday. Take what you need, And be on your way and, Stop crying your heart out.