How do I ask my roommate to leave for a short time?

I think you did a good job with your own answer. Just explain to him that you have a few things that you would like to do and need some privacy for a while. Give him ample notice. Also, just let him know that the utilities other bills around the house are getting to be too much for you by yourself and you need for him to begin to contribute __________$ per month. Otherwise, let him know that you may have to rent his space in the house for extra income. If he takes it personally, just kick his out. He probably should go spend some time with his mom anyway. Be firm, but considerate; after all, this is family.