I feel you. I just got done dealing with the EXACT same situation, here was the scenario:
The "woman" (I use that term lightly now) I moved in with was a coworker in a different department. I knew her awhile, and I needed a temporary (if you call 6 months temporary) living arrangement. She posted one day on her facebook page that she was looking for a roomie. I talked to her at work, she was hip to the idea, and we met a couple evenings later outside of work talk further. Mind you, this woman is younger than me, however, I was not interested in her in any type of physical relationship, not in the least.
We met, set ground rules which included respecting each other's private space (bedrooms off limits at all times), keeping the common areas clean, being respectful when having guests over, and keeping the place clean. We went to her place to check it out, it was a nice space, newer 2-bedroom apartment. Rent was agreed on, everything was verbal. Move in date was set.
I wasn't moved in long when I knew I'd made a bad decision. The weekend I moved in, I noticed that the kitchen had not been seriously cleaned since the day she moved in. Things that you can see during daylight hours that you can't at night. Checked the fridge and there was shit that had been in there forever. Science experiment sorts of food. So, decide to start out the roomate situation on the right food, and gave the whole place a proper cleaning. Like 4 hours work of cleaning. She got home, noticed, and thanked me. I said no problem, next time it's your turn.
Things were fine for a few weeks. I work like 70 hrs a week so I was rarely home. When I got home late sometimes she'd be up, we'd talk, seems she always had some sort of drama going on. She was younger than me, in her mid 20s. I always was a listening ear and tried to be a friend. When she was down, I'd try to cheer her up. We sometimes hung out outside of the hour, watch a football game, have a drink or two, dinner sometimes, not like dating, just friends.
Things started to go south pretty quickly. I was there a couple of weeks when I noticed she never did anything really around the house to keep the common areas clean as we agreed. She had a dog that shed pretty badly. The first couple of Sundays (my only completed day of the week off) I would vacuum and pick up the house. Mainly picking up, throwing away shit she had setting around. Didn't say anything about it for the first month. I'm a non-confrontational kind of person until I reach my limit or feel backed into a corner.
After a month one Sunday after vacuuming she comes home and I ask, "Do you have something against vacuums?" She laughing replies, "Oh I don't vacuum dude." I said that's fine, I'll vacuum, you are on trash duty (our apartment had a central trash compactor). She agreed.
So, as you can figure, that arrangement lasted about 2 weeks. Then it got to the point where I had to bag up our trash because it wasn't being done, I'd leave it outside the door and some mornings she'd take it to her car, others it would sit there a day or two until I couldn't stand to look at it and didn't want the neighbors to get pissed off. I'd mention it and she'd say "sorry".
Every month or so she'd have a party, always resulting in people crashing overnight. Wasn't a big deal as I knew the core group. First one they cleaned up. Second one I helped clean up. The next one occurred when I was away for the weekend, came home late on a Sunday and the place looked like a bomb went off (literally). That's when shit it the fan.
She wasn't there when I got home, I left it as-is and went to bed. The next day I got a txt apologizing for the mess saying she'd clean up. By the time I got home late that night the place was 'picked up' meaning the leftover trash was in two trashbags sitting in a corner of the kitchen. It was not cleaned up however, the kitchen was a mess, the living room was a mess. I worked 8am-11pm that week and went straight to work/bed so I gave her the week to get the place in order.
Woke up that Saturday, shit still wasn't done. Trash was still in the corner. Txt'd her to find out when she would be doing the cleaning. "Oh I'm away for the weekend, I'll get to it next week, btw can you take care of the dog?" At this point I'm in orbit.
I don't know what time she got home Sunday because I was asleep. Come home Monday night, she's sitting on the couch with her nose in her computer, nothing has been done. Mind you it's been over a week. I sit down and basically ask her "wtf??!", she says, "Sorry, I've just had a lot going on." I reminder her of our initial agreement about keeping the place clean, and that I didn't appreciate her leaving me with her dog without asking if I was cool with it. Told her that the place had better be cleaned by the time I get home the next night, if it wasn't I'd clean it and take 75.00 off next month's rent.
It wasn't clean the next night, so I stayed up until 3am cleaning. No clue where she was. Didn't say a word about it the rest of the week. Come home Saturday night and she's laying on the couch with a dude I'd never met. I go to bed, and I'm woke up at 9am the next morning to music blaring. On my only day off. At this point I'm done, and fortunately it lasted only 10 minutes and they left to go eat.
She got home that afternoon and I told her I was moving out, that she had 30 days to fine another room mate. Fortunately I was not on the lease, and I know you are and that sucks. I wound up moving 2 weeks later because I couldn't stand her snotty attitude toward me about up and moving.
So, in a nutshell:
1.) Tell them how you feel, and give them time to be more considerate of how you feel.
2.) If the above fails, speak to your leasing office about subleasing options. They've dealt with this type of thing before. Best thing would be to find someone to take over your portion of the lease for the rest of the lease term. Depending on your town and what part of town you live in, it could be hard or easy to find someone to take over. Post in Craigslist.
3.) Don't fight fire with fire. Don't be that person. Take the high road and do everything you can to get yourself out of that situation. It will not improve.
Hope all goes well!