I don't understand how it has been so easy for W to put behind our M, the 10 years of memories and shared value we have.
So Pack first you don't really know if this is easy for her or not she is never going to show you her true feelings. Second she has been probably detaching from you and the marriage for years and you just were not aware. Third it sounds like your marriage wasn't very good dur to the constant arguments and lastly she knows she can have you back whenever she wants. So right now she has a free pass to pursue other relationships.
There are many dynamics that I have learned in the last five years. Rejection breeds obsession, the one who cares about the relationship the least is the one in control and the pursuit and distance dynamic. You are experiencing all of these right now and it is mainly because of your belief that in order to be happy you have to be in an intact family. You have to change this line of thinking because it's simply not true.
