My hot *** girlfriend cant get me to finish?

I'm 20 years old and I've been going out with this very hot maxim model (really happy and proud about it) and we seem to love each other, but it seems like she cant get me to ejaculate during sex...so i last about 2 in a half to 3 hours then i try to use my own hand to finish. Sometimes i may Ejac during sex once in a while which is awesome. But the main problem is when she gives me Bj's..she does it so good on me but yet I cant FINISH!!! Last night it seemed like she was getting frustrated by it and just walked away I felt like crap... do you think this will effect our relationship? Do you think this is a big problem? I'm amazing at sex btw and i always make her squirt and orgasm..and she always tells me she loves my D*** so how much do you think it will affect me?