Can you guess what star sign i am?

I tend to get on particularly well with cancers. I can get jealous very easily. Im often described as being smart. I have a few close friends rather than a large entourage. Im very easy to get along with but very hard to get to know. Im often quite introverted until you get to know me and then all of sudden people question where ive been hiding the past while once i let my guard down and my personality emerges. I never tend to forget a betrayal and find it very difficult not to bear grudges. Fickle, narcisstic people really get on my nerves. Im highly strung and my bark is usually worse than my bite. What am I?