How Can I Live With My Mom & her New Man?

My mother's guy who I've known since age 8 and lived with since 2003 died 2 yrs ago. It's now me and my mom in a duplex. My mom then went online and met a guy in Feb. 2009. She had gone to his house for months, all of a sudden he's at our house overnight, almost everyday. I always did want her to go out with and meet new people and get a new man. But I don't like this guy. At. All. I think she just wants a man around the house. She even left the keys in the door, no dead bolt & the alarm. She wants a protector that much I think. But the thing is I hate not having the house to myself anymore, and I feel like its crowded there now. He may as well be living there. I told her I didn't like it and she said, "Its got nothing to do with you. I live here too." I want to go to the kitchen for food, he's there hanging around. I wake up, go downstairs to shower in the A.M. he's there. Some strange man in the house like that. Is it me that's being unreasonable?