I'm not going to tell my roommate that I own a gun and keep it in our house.
That sounds suspicious. What's the reason for not telling him?
I don't think it's any of his business.
I don't think it's right for you to keep the fact that you have a gun in your home from your roommate. People generally want to know when there are weapons in their home. I think you should be honest with your roommate about owning a gun.
I can't, I don't want to talk about it.
Why don't you want to talk about it? If he finds the gun he will be upset that you didn't tell him. It's better to let him know now to avoid drama later.