Gf never lets climax :( im thinking of just breaking it off with her and find someone who isn't selfish?

well i will try to keep this as brief as possible. my gf and i have been together long enough to take things "down town". there is one problem though, whenever we make love , she usually cums first and sort of kicks me off and i have to finish off myself (spank the monkey) and on those few occasions that i climax first i make the effort to at least go down on her till she climaxes too, i would really love to simply roll over and grab a beer, turn on the tv and leave her unsatisfied but i am not that kind of guy, i have tried to talk to her about this but for some reason her behaviour isnt changing. now i whenever she wants to have sex i make some excuse so that i dont have to get kicked off again and i just watch porn and jerk off just to take care of my urges. however she began to wonder and thats when she brought it up, she basically said " in most relationships its the woman who doesnt get to climmax, so i shouldnt be making such a big deal out of this " and i told her calmly that if she wanted to be like that she could keep her vagina herself. anywhere somehow she got offended and frankly i have no idea why, oh and will be a jerk if i decide to leave someone who isnt willing to pleasure me as much as i am ?