I was in a similar situation recently, feeling very guilty that my feelings toward my FD (now AD) of almost three years were aberrant. I just have a very difficult time bonding with her in the way that I want to and the way that she deserves! She has been with me since she had just turned 4. Her manipulativeness, lying, sneaky behavior made it really hard to feel that deep parent/child love bond. I felt/feel terrible about this. Her behavior is such that if she senses someone softening towards her she sees it as a weakness and will take advantage of it
She has been in therapy since she was first placed with me and our (wonderful) therapist has told me that "as long as it took for the damage to be done, that is how long it can take to undo it"! Yikes! That means another year! LOL
Anyway, I was feeling very guilty about this until I finally was able to speak the words aloud to a friend who is also a foster/adoptive parent and she told me that she felt the same way about her AD, for a LONG time, and that it has only been fairly recently that she has been able to feel that bond. So, I have hope! I would also recommend maybe talking to a therapist yourself, about these issues. Have you? I talk to ours and it has helped, but I still struggle
Anyway, I hope this helps, at least not feel you are all alone, I think it is really common, just difficult to speak about. You have my prayers and sympathy. Good luck!