Be nice to the woman who is going to inherit all your Dad would have left to you! You better believe she will at some point either marry him, or if he gets a weaker mind going, as sadly so many older folks do, she will probably convince him to write a will leaving her most everything and cutting you and all family out, since she "took care of him in his old age". It is a sad reality that more people will let the greed in their nature overtake any feelings of "what is right".
Older women worry about security, and financial security plus a place to sleep are top of that list.
Unless she is very well off now, she will be moving to to gain financial control of your fathers assets in time, and it will be done quietly. Best thing you can do is talk with your father about your concerns as diplomatically as you can. In the long run, it's his decision but if he wants to make sure you are taken care of, he needs to do that sooner rather than later.
My Father remarried after my Mother passed away, but he got a pre-nup, setup a will, and both are in the hands of his lawyer guaranteeing his estate split between my brother and me. (his wife is pretty well off on her own and her estate will go to her children).
This is a case where prevention and planning avoid years of hassles and bad feelings later.
