You've got two choices, you either accept that your feelings are not going to get better and you'll then need to accept your relationship is over because it is never going to be a good one whilst you actually feel hatred towards his daughter.
Or you can try to understand where things have gone wrong. You say that you used to get along with her and it is only in the past 12 months that things have changed. What has changed? If you managed fined for 2 years, then there is hope to rekindle what you had. Could she have a delayed teenage angst?
There have been times when I have found it hard to love my kids, when they were at their worse of teenagehood, but I couldn't hate them because they are my children and it's ingrain in us to love them. I might have hate them at times if they weren't mine. But behaviour changes, and my ds who made me so angry at times, who I thought had just turned out a lazy, selfish, unmotivated, uninterested, dirty person, is now the exact opposite. He is lovely, caring, fun, attentive, communicative and I genuinely look forward to spending time with him.
Your words towards her were outrageous and you might need to consider that your own attitude might have contributed to how things are now. In the end, nothing good is going to happen doing nothing, so either you try to consider what you can do differently, with the help of your oh, or counselling, or you need to accept that this is not the long term committed relationship for you, however painful this is.
I do feel for you though as ultimately, you would have built your life with your oh on the basis of her being a non resident. It sounds though as if you were ok with her coming to leave with you though, so you really need to reflect as to why things have gone downhill from them on. Resenting her mum has no place here. Sadly, her mum giving up on her might very well be why she is acting the way she is. However a pain kids are, unless they become violent, parents shouldn't reject them when it suits them.