I wanna cum in my girlfriend.

Me and my girlfriend have sex often and we get so horny that it is hard to stop. Now I last a long time and she last alot shorter than i do but yet she always wants me to fill her with cum and i want to do the same but everytime i get close she either gets sore or tires out right before I finish in her. Now she hates oral so much that she doesn't even like me eating her out so there isn't much foreplay we can do because her hand jobs are lacking. Now I love the thought of filling her up until my cum spills from her but I can't do it. I wanna know is it normal for me to want to fll her with cum or is it just because I never have done it before.