I almost killed my gf cat today

We live together. Cat is notorious for chewing on and ruining power cords (fire stick thin cords). He’s also notorious for ruining furniture. I told her she needs to either get rid of him and or get him declawed to take care of at least half the problem. She thinks declawing cats is inhumane. We have been keeping him out our room as best we can so he doesn’t bite on the cords. But today he snuck in on me. Which he is very good at. And I turned on the firestick to settle in while going to sleep and it went out all of a sudden. It came back on for a sec then went out again. I look over at the tv stand and notice him behind it chewing on the fire stick power cord. Chased him out the room not before I got a decent hand on his behind. Come back to realize the cord was completely ruined. Wanted to kill this cat seriously. Now I work nights and bring fire stick with me for when it gets slow. But the girl friend insists I buy a new power cord to bring to work instead of replacing it with hers cuz she said it was my fault for letting it in the room. How the hell am I responsible for a goddamn cat that isn’t mine sneaking in and ruining my stuff?