Jrt's and cats

by aj
(canada)

I have a one year old jrt and a 7 year old cat. From day one my cat didn't like jack my jrt. I tried to get them to know one another and things weren't so great from the get go. As soon as Jack started barking that was it, my cat was afraid.
Lately, since he's been neutered about a month now he's been running upstairs which was off limits to him from day one. He's always respected our rules since that is her place to be, not his. But his getting neutered has shown a different side of him.
I have put her on my bed, and brought Jack up on the bed he would just stare quietly and then there was a moment that he had me fooled and lunged towards her. Not good, not good!
Tonight we were sitting in the kitchen and Jack off and on was darting up the stairs. My cat came down thinking that he may have been put away for the night and jumped on the kitchen stool. Jack was 3 feet away, when she meowed I was horrified, picked her up as I knew she wouldn't have time to run and she clawed me good with her back claws and went to make a run for it. Jack grabbed her with his teeth, pulled out a tonne of hair and my heart stopped. Thankfully there was no harm done to my cat, but now I am determined that he is out to kill her. Help, what do i do?