Key to the house you live in.

So here is the situation.

I just got married and moved in with my wife who was a single woman with children. We dated for many years prior to marriage. I now pay half the bills and the bulk of the rent, as well as help provide food. She has three children, I have two. Two of her kids are over 19 and one no longer live with us. Her and my youngest sons do live with us, both are teens. Her second oldest who is 19 comes and goes at his whim. He had a house key which I found while doing laundry. I gave it to my wife.
Now that we are married and living together and I am paying for over half the expenses, I requested that the key her son had, be given to me. She told me that she did not know where it was.
I used a set of nail clippers off of her night stand to trim my nails and noticed the key sitting in the tray next to them, so I put it in my pocket. Being one of the responsible parties for maintaining the home, I feel that I am entitled to a key. I also went and had a duplicate key made. I did not tell her that I took the key or made a key. I figured it was a moot point.
She claims she did not know where the key was, yet when it was no longer there, she asked if I took it. I told her I did. She asked for it back and I gave it to her. A few day later, she asked if I had made a duplicate. I did not deny doing that either and answered her honestly.
Now she says that because I took the key and made a key she wants me out and wants to file for separation, because it was "not mine to take". I beg to differ. We are married, we live in the same home and I am entitled to a key to the house.
It is fairly evident that she did know where the key was, or she would not have asked what happened to it. Based upon that, she either did not plan on giving me a key, or, she wasn't prepared to give it to me yet. In either case, it seems to point to a control issue she has.
I am not saying I was right by taking the key without telling her and/or making one. I do however believe that if she really intended to give me a key, that she would not have had a problem with me taking it or making a duplicate however? Also, I was honest with her about doing it.

Now that I have explained the situation, I would like to hear others thoughts on this? Was I wrong? Am I not entitled to take the key and/or make a duplicate? Oh and yes we RENT, neither of us own the home.