Roommate gives roommate a key to shared apartment, allowing her access when no one else is home despite other roommate's wishes: 'I made it really clear that I don't want her moving in'

In the world we live in now, it's hard to find a place to live all to yourself. Rents are too expensive to be living alone, so that's why so many people end up having to find a roommate. Besides, if you're moving to a new place, it's good to have a built-in friend as soon as you get there, anyway. Part of having a roommate is maintaining good roommate etiquette, and it's good to find someone whose lifestyle lines up well with yours. Are you a messy person? Are you a night owl? These are all things that might make a difference in helping you to choose the person you'll be sharing your living space with.
 

If you live with someone long enough, you're sure to get a full understanding of their quirks and habits. Sometimes, however, a person can surprise us, even years into living with them. One man experienced just that, when his roommate of five years got a new girlfriend and suddenly spent all his time with her. So, is it in this man's right to draw some boundaries as to when his roommate's girlfriend can be in the house? Or do they both have the right to do what they want with the space they're paying for?