Both you guys have similiar situations to mine. Was dating a nice gal for about 1.5 years that had low self-esteem also. Tough to explain how she was, other than she'd often see things I did as attacks on her/her character, when in fact I never had any intentions of such. Led me to feel very unappreciated, and her feeling very excluded.
She moved in with me back in June, and I got the notion in July to buy a house. So, I did - solely on my own. I told her that while it would be my house financially, that I wanted to share that with her to make it our home. Should we get married one day, she would gain the financial aspect of it then, but it would still be her same-old home. I don't know that she understood this completely. She never took any pride in the house, or pride in me for achieving it. She said that she always felt as though she were living in someone else's house, despite my encouragement for her to set the place up, decorate as she would like, etc. She never seemed to get the motivation to do any of that stuff, and when I would step in and do something (got tired of living out of boxes for a month), she would get upset with me. She became very possessive of the things she officially "owned".
Things became so petty and we bickered non-stop. A couple of extremely petty examples stick out in my mind. Imagine the setting - her entertainment center - for the most part setup in the living room. The one thing that remains to be done to it is to mount the glass door on the front of it. My hands had already been slapped for hanging pictures, or any of that sort of thing, so I, milling around one evening looking for something to do, figured I'd just make myself useful and put that door on - was tired of it leaning up against the wall. The mounting hardware had been packed away previously, and I asked her if she had found it. She said that she had - but that she wanted to be the one to put the door on. I thought that was funny, but didn't argue - just told her that if she felt she needed to do it - no problem. It didn't happen that day, the next, or the next. After several days passed, I asked her again and we fought over it. She basically told me she didn't "trust" me to handle the job without breaking the door, and that she thought my time-constraints to be unreasonable. I'm no Oaf - and I have my own entertainment center w/TWO doors in it - so I have the experience down. Does anyone else move into a house and spend a month before you set up your living room furniture or hang a picture on any of the walls?
One more - sorry if this is boring you, but I'm only trying to provide entertainment at my own expense.. :/
She put all our food away in the pantry in an admirable fashion. One day weeks later, I was looking for a particular canned good. The cans were in a large stack on top of each other, making searching difficult. I remembered that I had some lazy-susans (spinning trays) I could put some of the stacks on - allowing us to rotate the food and access it more conveniently. So, I threw a few of them on the shelves in the pantry. She's pissed about it.

While I saw it as myself just adding my part, she saw it as me attacking and tearing apart her work.
I began to pull back from her emotionally. She began to tell me that she felt she wasn't being allowed to participate in the relationship and that I wasn't meeting her needs. I was at a loss for words as I felt that I had only offered her encouragement and support about the things she wanted to do ranging from school/career to decor, but that she never seemed to look at me with more seriousness than what one would give an 8 year old child. The petty things drove that home -- the feeling of lacking respect and appreciation.
We decided to split. It was mutual, but if it came down to brass tacks, I suppose I was the one that asked her to move out. When I did, she responded with the fact that she had already looked at some apartments, so the handwriting was not only on the wall - it was flashing neon colors.
It took her two weeks to get into the apartment she'd found. During that time period, our relationship was just like old times. We were loving and supportive of each other, didn't bicker and fight. It seemed like all the pressure was off - but really I saw the change in her. I never felt any "pressure" from the get go, but it seemed that maybe she had. This, of course, all made everything much more difficult - reinforced the positive things about our relationship, but she had signed on the lease and we had gone past the point-of-no-return.
I saw her lastnight. Went to over to her new apartment to help her set up her computer. She took me out to dinner. We got back and I went to work on her computer, she started back-seat-driving. Now, computers are my profession, and she knows very little about them. She started to suggest that some of the problem she had with it were because of the things I had done to it - which I knew to be totally inaccurate. The bickering was going to start, but I resisted, finished the work, grabbed my things and bid her goodnight. She was somewhat shocked - I don't think she understands the image she conveys to me.
I find myself so confused from time to time - I honestly miss her. I think you said it correctly Goat - we were more in love with the idea than anything else - and that is what I'm missing. Af far as my lady -- we can't communicate w/each other effectively. I don't know that I'll go back or call her.. I'm becoming more convinced we don't stand a chance at getting along. At any rate, I'm sure you're tired of reading about this petty crap that isn't worth all the effort of busting up a relationship over, so I'll just say "Thanks" for letting me vent and ramble on like a madman... ...
Sean...