Ah, well these details expand significantly on things and shift the light quite a bit. I think I've got a much better understanding about your situation. When you move in with someone, the dynamics of the relationship change; some things are better, some things are more difficult. But, if it's a relationship that's going to work for the long haul, you'll generally know it. It definitely sounds like you realized that things were not progressing as you'd expected. At the very least, there was a fundamental problem of the two of you being able to work things out. The key to a relationship is not that fights hardly ever happen, but that when they do happen both people are able to work it out and not leave stuff unresolved all the time.
I've known a number of people who lived together for years before getting married. It's a different story for women than it is for men, as I've come to learn. Most of the time, women need reassurance that the relationship is a lasting thing, something with definition. Casual and soft definition is usually more comfortable for men. Not being ready for marriage is "now"... it doesn't sound like you are averse to ever doing it, just not in the short run. I'll bet anything that her learning of your plans about marriage dramatically changed things for her... this put her in a position of ambiguity about where the relationship would be going. And I tell you, that left hanging out there will erode the trust of a relationship. And it sounds like that happened... emotional distance eventually becomes physical distance.
Mid 20's is an early age in terms of relationships. You don't have a long stretch of relationship experience at that point. It takes time to learn the ins and outs of getting along with someone. And she was unable to really express her discomfort on not being able to see a clear future with you, or trust that taking things slowly would eventually lead to a better understanding of where the relationship will go.
From what you say about her, she has some fine qualities. Who knows, if the balance of needs between you was better, maybe it would have worked? Funny thing, though... although I know TV comedy shows are all fiction (though some based loosely on reality), you should check out "How I Met Your Mother". There's this stretch of time were a guy named Ted is determined to find his wife to be. He meets a girl named Robin and starts thinking that she is the one. The move in together. But there's just one problem--Robin is not really sure about getting married, if ever. It's just something not a priority for her. But Ted wants to see a definite path to marriage and can't really put up with it being ambiguous. Eventually they have to break up... because that conflict puts too much stress on the relationship. I think there's a lot of truth to how they portrayed this, although the reverse is probably more common (the woman having plans for marriage and the guy wanting to keep it on the back burner).
I think you made the right choice, though... and handled it well. Don't let the craziness of her parents get to you. They're being unreasonable. It's not "your fault"... sometimes things just don't work out.
