Dear Kat: I'm a single girl with a female roommate I met through our graduate program. Sometime last year, I hooked up with a guy who was also in our program, and we talked and hung out for a while, but I wasn't interested in dating him, so I let the relationship go. I graduated last spring, but both of them have at least a year left. Somehow this guy and my roommate became friends since I left the program. Now he comes over sometimes, and they hang out a lot. She knows we hooked up and only invites him to the house when I'm not there. I find out about it through pictures on Facebook or people telling me about the great party at my place. I'm really not comfortable about this, but my roommate has a right to be friends with him, right? I'm not her mom and can't tell her not to invite people over, but I don't know what to do.
Dear C.R.: You're right. Your roommate does have a right to be friends with anyone she wants.
In my world, hooking up with someone your friend or roomie hooked up with is completely taboo, but some people don't find that to be a problem.
Think of it this way: If she had an acquaintance who came over and did illegal drugs that you are completely opposed to or was a violent drunk or stole things, you'd have no problem asking your roommate to bar that friend from coming over. (Or at least I'd hope you'd have no problem with it.) You'd be uncomfortable with having that person in your house, regardless of whether you were there.
Even though this is a slightly more gray-area issue than illegal or violent activities, I don't think you're overreacting. My motto is, if you feel uncomfortable or unsafe, you have a right—nay, a responsibility—to do whatever it takes to change that, especially in your own home. Call a cop if you hear a scary noise or someone is acting crazy nearby. Get someone to walk you to your car in the dark parking garage. Tell your roommate you're not cool with this guy coming over, regardless of the reason why. Trust your gut, even if it feels crazy to you. It's not paranoia; it's good sense. Furthermore, it's your house.
As an aside, your "somehow" tips me off that you're suspicious of their friendship. Remember, sometimes people just become friends in graduate school. But if it's jealousy or territorialism that's making you suspicious of their friendship (are you afraid they're going to hook up?) then you need to address that within yourself, too. It's perfectly natural to be jealous in situations like this, and you might just want to chat with your roommate about the nature of their relationship and how you feel about it, if that's the case.
In my world, hooking up with someone your friend or roomie hooked up with is completely taboo, but some people don't find that to be a problem. If that's what's making you uncomfortable, address it, however you can, and move on.
But regardless of his motives (or lack of motives) for becoming friends with her, or the reasoning behind your discomfort, it's your house. It's where you live. And it's where you need to feel comfortable.
You have to talk to your roommate about this, obviously. She needs to understand that you're not comfortable, and you two need to figure out a way to deal with it. Clearly this guy is going to find out somehow that he's not invited to your house, which could cause embarrassment for everyone in the long run, but really, that's not your problem. If your roommate can't respect your needs, regardless of what they are, maybe you need to find a new roommate.