Sometimes people pull away when they want to get closer. If she really did have strong feelings for you in the past (only you would know) then when she said that she was never happy, it was a lie. You know if she was happy before.

I think whats really bothering her is that she really wants a place with you. To some girls sharing a bed and cuddling are important. After talking to you about it maybe she doesn't feel like that you guys will ever get a place together. That would make her frustrated and that's a reason she might say that the relationship was a mistake. It seems like getting a place is something she really wants so my advice is at the least tell her that it's what you want too. If you can't get a place, spend more time with her, have her sleep over more often, and let her know that in the future that you guys can live together.

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"you know my name, you know my face, you'd know my heart if you knew your place"