I'm going to change the wifi password on my roommate
Why are you changing it?
I don't want to share my wifi password with anyone.
Why have you shared your wifi password in the first place? Unless he was paying for your wifi, what is yours is yours and there are boundaries for people on how they use your things. While it's okay to not let them use your wifi, I still would recommend you talk with them to make sure they understand that it's yours and not for them to use.
I'm sleepy, I don't want to talk about this shit now.
It's cool if you don't want to talk about it. If it's your wifi you're free to keep the password to yourself.