I'm really upset with my friend because of things he's doing. Do you think I should stay this way?
Wow, it sounds serious. Is it? What has he done to make you so angry?
He threatened to kill his mom soon; that made me really angry.
If your friend is threatening to harm or kill his mother, then you should consider alerting the authorities, or asking his mother if she needs help. Threats of murder can be serious, so it is understandable you are stressed and angry.
She might deserve him to kill her though, she sounds horrible when he speaks about her.
It's still dangerous and harmful to threaten to kill someone. If you won't contact the authorities, maybe you can try to convince your friend to get help from a therapist to deal with his feelings in a safe way.