I feel like you're really overthinking this issue. I know many guys who have described the same issue you're having, vaginal stimulation not replicating the feeling of a hand. A few of them mentioned that masturbating with a fleshlight changed their life. The issue, from what I understand, relates to the death grip that some guys masturbate with. A vagina simply can't replicate that sensation, so forcing yourself to only get off through this type of stimulation using a fleshlight (and ONLY in this way) "resets" your dick in a way. A lot of people have sexual fantasies involving those of the same sex, and maybe your urge to be dominated could be fulfilled by your girlfriend. There are many toys out there, and role playing is definitely something explored by many hetero couples. Have a conversation with her about what you want and what you're curious about. In the end, if you feel as though the sexual dynamic is not fulfilling you, it's perfectly okay for you to end the relationship if you're not happy.