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What an odd thing to say! What do you mean that "she seems to be, for some reason, loyal to her husband." I feel like either you left something out that would explain why it would be odd for her to be loyal to her husband (like, she revealed to you that he cheated on her or something), or you just have no idea what it means to be married.
So let me tell you:
Being married means, ideally, you've made a commitment to a person to whom you will be loyal.
I had a crush on a married man once, but I never did a thing about it, because he was married and he loved his wife. And then I met someone who wasn't married, and I moved on, and that was the end of that.