<human>: Can you condense the text into a few key points?

So a quick explanation of my living situation... I live in a shared house between 3 other people. My boyfriend of 3 years, our mutual friend and another housemate. Tomorrow is the birthday party of our mutual friend. 

This friend told me today that their friend (let's call them "M") from another city is coming to visit and celebrate. They also asked me if it would be okay if M stayed over on the couch that night. I would normally be perfectly fine with such a situation, however M has had a previous sexual history with my boyfriend. M has had the decency of telling me about their history with my boyfriend in great detail, much to my dismay. 

I do trust my boyfriend not to have a fling with M, however it brings me great discomfort to have M in my house, let alone stay over. Some people do not click I guess. Also, I have a very important final exam on Tuesday. Having M stay over would not be that great for my concentration, considering how I prefer studying late at night. I would have the livingroom out of bounds from my use for that night or maybe two, so close to my exams. I'm not fond of the idea of an intoxicated M staying over in my house, given he's had a history with my boyfriend and due to it being so close to my exams.

Am I being irrational and clingy, or is this a genuinely legitimate reason to put my foot down and say "No, sorry I do not want this person staying in this house while I'm trying to study"? Our friend who is inviting M also said if I was really uncomfortable, they would tell M to stay somewhere else. However, there is still an itching feeling in me that says, if I tell them I don't want them to stay, it'll convey an image that I'm an insecure person.

Many thanks
<bot>: Boyfriend's ex is coming over to stay tomorrow night. I am uncomfortable and have important exams coming up. Is it reasonable to demand no?