Your father was absent from your life, while your sister was the center of his attention. In the competition for this very important male attention, you were clearly the loser. Your sister received attention from a powerful male figure; you lacked this connection. It is possible that your lack of connection with a male figure is directing your adult sexuality. Freudian theorists believe that women who did not feel loved by their father will attempt to gain that lost attention, in the future, with other men. Freud believed very strongly that the nature of a woman’s sexuality would be based entirely upon her relationship with her father. The theory goes as follows: women who feel rejected by their father continue to long for this attention and as adults will attempt to gain that lost attention. Sex is a powerful way to gain male attention.
Sexual addiction usually includes excessive masturbation. I am not saying that this is the only form that it can take but in my experience, I have never seen a case where frequent masturbation was not occurring. You did not mention masturbation in your letter to me: in fact your sexual behavior seems to be focused on your boyfriend.
While Freud can be criticized by modern theorists for some of his ideas, much of his theory has become foundational to other psychologies. You desperately wanted your father’s love and attention as a child and you felt very rejected and neglected by him when comparing yourself to your sister. Perhaps when you feel you need attention, or want attention you use sex as a way to gain that.
Sexual addiction? How much sex is enough and how much is too much and thus an addiction? Once a day? Twice? Three times? Five times? Generally speaking most therapists have no absolute number in mind but instead look at the impact of the sexual activity upon the overall wellbeing of the client. In other words: is this sexual activity harming the client? Is your sexual behavior a positive part of your life or it a detriment to your overall happiness and wellbeing?
If it is and after recognizing that reality you still cannot stop the very thing that is hurting you, then you have an “addiction.”
I would strongly recommend that you see a therapist because they can very quickly bring insight to this situation. If your boyfriend thinks that your desire to have too frequent sex with him is a problem, then your sexual behavior is endangering your relationship. Sex is a part of a relationship, not the basis of a relationship. What I am saying is that the relationship is more important than sex. Do what you can to nurture and protect your relationship. That would include having the sexual part of your relationship analyzed by a professional.
Good luck and don’t hesitate to write back.