Hi,
Thanks a lot for sharing your story. Healing is a long process. It is evident you are on the path of healing. But it takes time and sometimes it is bumpy. Perhaps therapy could be of help. I am not sure about bullying. But about your fantasy during childhood it seems to me that was a very logical way for your mind to defend yourself from external chaos. As a child you had been neglected and abused. Then you were introduced to new environments with multiple challenges. You were just a kid and those were huge challenges for you, you were just a kid and could not control almost anything that was happening to you . So, as a mechanism, your mind created this fantasy world were you were in charge. I think these fantasies are to bring some relief. In my childhood, I would fantasize about being a successful pianist, everybody clapping at my performance while in the real world my mom was always cold and criticizing me.
To me, your cruelty towards your pet during childhood was a kind of a release, and again, a way of being in control, to compensate for what had been done to you. This is what I thought when I read what you wrote. I am not sure about my take on these details of your life but I think it is very unfair you feel guilty for them . Those were reactions that you could not manage, really.
Anyway, I hope you keep posting. I have faith in you and hope you will feel better