<human>: My roommate and I moved in together a little over a month ago without previously knowing each other.  The first weekend at the new place, he had a girl over for the weekend.  I didn't talk to her much, but she seemed nice, albeit a little strange.  

He later informed me at a bar that she was his ex of several years and that they hadn't been together for over 2 years.  He told me that she was very possessive over him and jealous of any girl that he interacted with, and she still is like this to this day.  He says she hasn't quite grasped the notion that they will never be together again romantically.  He also informed me that she has a history of violence and during an argument during their relationship, she stabbed him with a kitchen knife (for which he never pressed charges).

She came over this weekend again and knowing this information, I'm not comfortable having an unannounced guest come over who clearly has serious problems and is clearly not ok with him having female roommates.  In addition, during this visit, I have overheard her talking crap about me and she has been using my dishes without permission and leaving the apartment a mess for me to clean up.  Overall, I find her presence discomforting and lacking any kind of respect for my home space.  Is it irrational to ask that she not come back to our apartment?

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<bot>: Ex-gf of my roommate has a history of violence and irrational behaviors and I want to tell my roommate that she is not welcome in our apartment.