Getting a rooster a friend?

I had 3 chickens, 2 hens and a rooster. The 2 hens got sick. They suddenly became really weak, and it looked they were paralyzed on one side and they were just flopped to the ground. One of them died then the rooster killed the other one (putting it out of its misery I think) . If anyone knows what happened, it would be appreciated! But the rooster survived. Our previous chickens made friends with the neighbors cat (yes, I have had very strange chickens in the past ) but my rooster is aggressive towards other animals but I think he's lonely. I don't want baby chickens and I'm afraid if we get him another rooster that he'll kill it! Any suggestions to what we can do for him? He's a pet chicken by the way.