A lot of women are attracted to dominant, bad-boy, alpha-male types sexually. The problem is, long-term relationships often become emotionally unsatisfying or even abusive. It's why you see the classic stereotype of the girl who dates bad-boys in her teens, 20s, then eventually wants something more stable and emotionally supportive, so she ends up with a more even-tempered, gentle, even submissive husband.
It all comes down to the individuals and the dynamics of the different relationships but I would guess a lot of times, the women will want to remain with the stable, supportive partner, while the dominant male is mainly just sexual thrill. She may even grow bored of the latter eventually. The danger would be a women who has never been with a man like that and is so consumed by the sexual thrill and giving herself to this man, that she deludes herself into thinking he can also provide the other side of the relationship. It sounds like your GF has already realized this isn't the case and so it seems unlikely she would leave you but you may still have trouble navigating what your sexual relationship is with her now - sounds like you've made progress though.
If its any consolation, I had the opposite experience with my first really long-term GF or 8 years, where I was kind of the bad-boy and she was very submissive. There was a point through college where I wanted to have experiences with other women but my GF begged me not to break up with her and I felt bad, so I stayed with her but I became resentful and kind of neglectful. Eventually she had enough, we broke it off and she ended up with a guy she worked with who seemed like kind of a vanilla, "good-boy" type but he provided her with the attention and more wholesome life she wanted. She told me she really enjoyed finding that she could be the dominant one in the relationship.