The only chance you have to knock any sense into her (secondary and relatively unimportant at this point) and holding onto your dignity (primary and very important for your self respect) is taking this position. The other one will make you look so weak that any respect that may be there for you will disappear. This stand will allow you to hold onto your dignity no matter which way it goes.
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Take a stand and take it NOW. Don't wait, don't hesitate. I know the fear that wells up inside of you when you look at this option, but it's the only option that will save YOU. If you don't do this, you will regret it for the rest of your life. You will be comprimising your values, your dignity, your right as a man to stand up and not accept unacceptable behavior.
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Don't take the 'easy' road of non-confrontation and drawing a line in the sand regardless of the outcome. In the long run it will turn out to be the hard and painful road. Take the road less travelled and you will be glad you did - because when you look in the mirror you will know in your bones you did the right thing as you have been doing. Dont' compromise yourself out of fear of what you think will happen.
You don't know what will happen. Stand up for yourself and life will unfold as it should. Be strong, be corageous (courage is having fear and going in spite of it), keep your self respect. She will respect you more for taking a stand, and if she doesn't, you will respect yourself more - and in my book, that's the most important thing.