He's jealous. If she had the cat before you he feels like your invading his territory since your a man. I had the same problem with Thomas-only he didn't take it that far. When I first got Thomas, my bf had a job but I did not, so he got used to me being around all day and not having to share me with another *Man*. When my bf would get home, if we tried to snuggle, he'd inch his way in between us. Sometimes he would just randomly go up to him and bite him and then come back to me. But Thomas got used to it though, he knows he's number 1 in my life lol
But yeah, animal's can sense fear. If they know your scared they will go with it. Don't put up with it. Maybe your partner could help you out and start punishing him when she sees him bite you/attack you. He's likely to see her as more of an authority figure since she's his owner.