<human>: My roommate (whom I've been friends with for 5 years) and I moved into our place a bit less than 2 months ago. I can count on one hand the number of nights Girlfriend has slept somewhere else.

She does not live here. She does not pay rent. She does not chip in for the bills. 

Our landlord has given us (i.e. me, because my roommate never answers her phone when it's the landlord calling) a bunch of crap about her being here all the time, and has expressly told us she doesn't want a third person living here.
I don't either. 

I don't necessarily dislike this girl on her own merits, but the fact that she is constantly here is grating on my nerves. They tell me all the time that it's not awkward for the three of us to hang out, and maybe it's not awkward for them, but it is for me. I'm starting to avoid hanging out in my own living room because I can't stand watching them be all couple-y all the goddamn time.

I'm also annoyed about the fact that my roommate clearly knew that this was going to be the situation when we moved in, but simply neglected to mention to me that I would  be housing a third person. I'm basically starting to get the feeling that I'm only here to finance them being able to have their own place, because Girlfriend can't afford to pay half the rent.

I did mention to my roommate the other night that I have a problem with Girlfriend living here, but it's honestly like I never said anything because exactly nothing has changed. I imagine this might be because they're able to convince themselves that she's not living here, which is genuinely beyond me. Eat, sleep, shower, spend all your time when you're not at work? You're living here.

I really don't want this situation to escalate any further, and I definitely don't want it to turn into a fight, but I'm afraid I won't be able to properly explain myself without it becoming 2 against 1, Girlfriend getting all offended, Roommate getting upset on her behalf, and costing me my friendship with my roommate, and probably eventually my living situation.

Provide a brief overview of the text.
<bot>: My roommates SO is living at our place against my and our landlord's wishes. How do I get her to be around less without it sparking a huge fight and ending my friendship with my roommate?