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Permit me to be among the first to tell you how shallow you are -- at least in the ways of love. You are not in love with her, you are infatuated with, and fixated on, a place in your mind where you construct her untainted image.
You fell in love before you had ever interacted with her. To your misfortune, and perhaps eventually hers, meeting her and talking to her didn't spoil the effect.
That you don't understand why she wants to be faithful to her husband is a sign that you should not enter into any deep relationship for a while. Who could trust you?
Since you think you really love her, then you owe it to her to spare her from yourself. Get out of her life now, in a kind and gentle way. You owe it to yourself to learn to love a person, not a phantom of your own design.