There comes a time in some lives where there is no longer what anyone would consider a "good quality" of life. Once that quality of life is gone it is normal for us to wish our loved ones relief. I did that with my grandmother who died of lung cancer and my uncle who died of AIDS. There is only so long that you can watch someone you love suffer before wishing them relief. It is not a bad thing to do so, but rather I see it as a loving reaction.
So sorry to hear that you are experiencing this. My heart goes out to you.