I've had to read quite a bit on D/s, and sympathize with both perspectives. Yes, it's fucking insane, and yes, some people honestly want it. The same goes for polyamory, perhaps?
A D/s relationship, even a 24/7 one, can on the outside look like nothing particular. Not everyone in M/s dynamic will be wearing collars, not everyone in a power exchange relationship incorporates elements of BDSM as in whips and chains into their life (that was a surprise to me). Those kind of relationships might resemble traditional patriarchal marriages , with the exception that gender doesn't predetermine role. It doesn't mean that the slave will never stand up for themselves - just that after hearing their arguments, the master will ultimately make the decision.
That said, most TPEs seem to have an hour a day or a similar safe space practice where roles are discarded for egalitarian communication and voicing of wants and concerns. What little I understand of submissive's needs is that they want to give up control of some or most parts of their life to another person whom they trust. It doesn't have to be sex - it can be stuff like finances/spending money, diet and health/exercise, self-improvement etc. It's from there on the top's/dominant's/master's responsibility to see that their partners needs are met in that area in the best possible way. I've even read that dominants understand that they don't have needs, only wants, and that they can but those aside to take care of the needs of another person. And subs are different, too - some take greatest pleasure in obeying their doms, especially in doing stuff they wouldn't normally do, others want to please their partner and bask in the approval and surprised delight, some relish the possibility of a simpler, more stress-free existence.
That said, in my relationship with VanillaIce, we are not really into roles, safewords etc. It's not roles for us, and thus creating a separate fantasyland we would need to depart from to have a frank discussion isn't needed - if somebody wants to stop, have a time out, or talk about something, they just open their mouths and blurt it out. Like in a normal relationship, if somebody in the middle of sex says "Stop, I need a breather", you stop and give them a breather. BDSM is not something I would do of my own volition, but I have devoted myself to my partner, including accepting, supporting and trying to cater to all of her needs, wants and desires.
Back to OP: are you under orgasm control? If so, then your gf is just a self-centered asshole and you really need to talk about lifting that.
Me: bi female in my twenties