<human>: I moved in with my brother and one of our mutual friends to save money about a year ago, at which point I didn't mind his girlfriend at all. As time went on, I saw how she demanded him to do *everything* for her and she did nothing for him in return. I can't even look at her anymore, it makes me sick. I stay out of it, though, because my brother loves her and I don't want to put a strain on my relationship with him. As time has gone on, it has made me think less of my brother and my hate for her has continued to grow. It's an extremely toxic situation that has given me more anxiety than I can handle. 

For Valentine's day, my brother gave her a key to our apartment. She has been using it daily and just hanging out in our apartment, like she lives here too. My brother is going to graduate school an hour and a half away and lives there during the week and here on the weekends (and drives back one night a week to see his girlfriend). She watches tv, leaves all the lights on, takes showers, takes whatever she wants out of the fridge and just generally feels entitled to this space. I am not ok with paying for her to lounge around in my apartment when she is perfectly capable of doing so in her own. It's especially frustrating knowing that my brother won't be home for days.

I woke up this morning to her shit scattered about (her laptop, bags, papers she's grading) and all of the lights on in the house and I just broke down crying. I don't know what to do. My brother refuses to acknowledge that his girlfriend and I don't speak, to avoid confrontation with us, and it makes dealing with this situation very, very difficult. He's extremely sensitive toward criticism about his girlfriend because she is constantly worried and insecure that people hate her. 

How do I delicately handle this situation without hurting anyone's feelings? I'd love to tell his girlfriend that I don't appreciate her being here, but she will cry to my brother about it and I'll be ostracized from his life even more.

Provide a brief overview of the text.
<bot>: my brother's horrible girlfriend was given a key to our apartment and has taken advantage of it. How do I get her to leave without straining my relationship with my brother even more?