Hello- Thank you for asking the question. I have over 30 years of experience working with individuals, couples and families & am happy to reply.
I am sorry to hear about what has happened in your marriage-
Are you available to chat now?
In reading what you have written, and rely on my 35 years of experience of working with couple, it appears that your wife has little or no interest in working on the relationship and has thus detached herself in a way where she is only being more and more provocative to achieve whatever secondary gains she may have in mind toward ending this marriage.
First and foremost- you have to keep in mind that the only person you have control over is yourself and although this is a time where you feel devastated and want the marriage to continue- if there is no motivation on her part, you are going to have to seek some counseling for yourself to sort out YOUR path and direction at this very difficult time.
There are never any concrete answers to all of the WHY question you have as each person is as unique as every relationship.
I am going to give you a link with some excellent, detailed information on infidelity and recognizing traits that signal the end of relationship. This will help you learn but it won't end the pain. This is a difficult process and as above, one in which you may need professional counseling to help resolve.
Qualities of success vs unsuccessful marriages:
If you have additional questions, feel free to ask- I am happy to help at this difficult time.
Kindest regards, Bill