I don't mind the graphic details (we've had plenty of graphic sex stories shared here, no big deal), but I do have to say that I think you're placing way too much importance on whether she cums or not. It sure reads like she is, but so what? Sex can be enjoyable without cumming, too. And focusing so much on getting to climax can take away the pleasure of sharing bodies and experiencing the sensations going on in the here and now. The question to ask is, "are you happy and satisfied?" As far as believing her or not, just keep reminding yourself that she is a different person, not your ex.
Many women can cum multiple times very easily, while others take a much longer road to get there. The ones who hardly ever cum or aren't sure (because sometimes it's a Little O, not a Big O), are often wrapped up in the thoughts or insecurities in their heads - women think a lot during sex, much more than men do.
Regarding your ex having lied about not having orgasms, well, that's just what a lot of women were taught to do in our highly repressive society. If we don't cum, we are shamed into thinking there is something wrong with us, and if we want sex a lot or for our sex lives to improve, we are made to feel like worthless sluts - so who the heck would speak up if they were not able to climax easily unless they were able and ready to question all that and pursue satisfaction.
In a way you are contributing to that mindset with your current gf, by making whether she has orgasms or not so important. RELAX and enjoy what you've got and just keep reminding yourself to stay in the moment and that she is not your ex-wife.