I got a new flatmate two and a half years ago, and we have been a couple since the week after he moved in. It seemed silly to throw him out of the house when we started going out, so we have been living together since the very beginning of our relationship.
Now we are considering marriage, and I wonder how our living together will help or hinder us.

That is question one, question two concerns the fact that throughout this time I have been working on a particularly unsatisfying PhD which I am considering quitting. If I don't quit it will take a long time to finish. I often feel as if my relationship is the only aspect of my life that works properly, but wonder if it would seem so ideal if I were happier with my work (does it only look good because everything else looks so bad). Should I wait until the PhD is gone, one way or the other, before I make any binding decisions (eg marriage), and should I keep living with my partner through this time?

Thanks for any advice

Have you discussed any of Dr. Harley's concepts with him? If so what does he think about all of Dr. H's views and suggestions? It'd be a good idea, no matter what you do to find out how much of this program he is willing to follow first and how well it goes.
It could be that you feel the way do about your relationship because of the way your career is going. But it could also be that you feel the way you do about your career because of your relationship. Just take time to weigh and balance things. Don't make any hasty decisions. And by all means find out where he stands on all of Dr. Harley's work -- IN ACTION, NOT JUST VERBAL AGREEMENT!! If he ain't willing to work on it while you all feel "in love" then he sure won't be willing if you get married. Men tend to feel they can relax then, even though women are just starting to become secure and start really working on things. So ther'll be plenty he'll still have to learn if you two did get married.

Best of luck!!

Becki