My Fiancee is Ana/Mia...Help!?

About a year and a half ago my girlfriend (now fiancee) confessed to me that she was bulimic. I accepted that she had not exactly been "lying" to me, per se, but was definitely hiding the truth from me and promised to support and assist her in any way I could. She promised that she would stop doing it and we came to an agreement that she would stop doing it and I would support her and help her, and that she would stop, with help from me and her family/friends. For about 1 year all was well, and I thought a new leaf was turned and we had gotten over this stone...

Or so I thought...

She had been "secretly" purging behind my back the whole time and was, again, trying to hide from me (although, if you know someone who purges, it's pretty obvious) that she was still purging, and clearly had no intent to stop. She is getting so brazen, now, that she doesn't even make sure all of the "junk" in the toilet is gone after she purges, and I lift the seat to use the bathroom and discover particles of dinner in it (sorry for the description; I tried to be as PG as possible). I have encouraged her, time after time, am loving and accepting of her body the way it is, and have offered to help her to cover the co-payment of her going to a local, critically acclaimed and nationally recognized treatment program. Even though I have very little money due to being unemployed she still seems to not want to get better.

What's worse is she is constantly nagging on me about the bad things that I do, like smoking, and drinking, that I have given up as a plead for her to be healthy, do the right thing, and get help, but she has this strange rationalization and justification of her addiction of purging as being better than my former habits. She tells me "one day of my (former) smoking is equal to one month of her purging" and it just bothers me that she thinks that way. I have gotten her the number to the local (again accredited, well recognized) eating disorder program and she says that she has called, but is not seeking treatment.

And now for the very disturbing part....yes sadly there's more..

I recently had to purchase a new computer because our laptop died. I opened up a line of credit to buy a computer because I am attending college again for I/TT and needed a home computer for school. I am very protective of this new computer because it is an integral part of my education and am leery of viruses and other stuff that can corrupt my brand new computer, that I couldn't afford to replace, again. My computer was acting funny and, being an I/TT computer science major, I decided to use my skills to fix it. Well, as I said, already being wary of the potential danger to my new computer, and doing everything in my power to protect it from getting damaged, I had at it. In the course of my actions, my curiosity got the best of me, so to speak, and I found a lot of disturbing things on my hard drive. There were several pictures and movies of gruesome, repulsingly and disgustingly thin, emaciated, women that had been downloaded to my computer. There is only 2 people EVER that have access to this computer and, by process of elimination, it was not me. Don't get me wrong, I don't distrust her; she is free to look at whatever she wishes to online, and I know that she knows what this computer means to me, but she doesn't seem to correlate the health of my computer to me getting a better job. I just feel that all of this "pro ana/mia" junk she is looking at is only fueling a burning fire and is creating a vicious cycle and supporting her addiction.

I really want to know is what is my next course of action? What can I do? What do I do for somebody who is refusing treatment and continues down the same path of addiction? How do I cope with somebody that is rejecting all of my support and not recognizing my sacrifices in attempts to help them?

And, worst of all, why should I marry someone who is constantly lying, or covering up the truth, or just doesn't care? How do I marry someone who has no concern about what I have given up in an effort to ultimately help them?