I cant get off during sex.?

[Nathan]

So last year i lost my virginity, went to many parties and had a good selection of partners. Summer ended, and so did my sex life at the time and i decided to stay single for awhile. 8 months later i get into a relationship with a girl i like alot and we are very very sexually active. Now heres my problem, from past girls and this one, i havnt once gotten off during sex. The other day i was determined and she was game, we ended up having sex 9 times that day with 30 minute breaks each time. Each time lasted 30-1 hour and a half. She was really happy the entire time, and i was starting to get bored because i couldnt get off no matter what i tried. We did different positions, oral, and i even went as hard and fast as i could for the longest time. Nothing. When we first tried to have sex i had trouble getting hard, the next time i was able to do so and it was on from there. I dont think im suffering from anxiety, im not really nervous or anything i just like to get to buisness. So any tips at all would be appreciated. I think after the first time ill be good after that, but i dont understand why its so damn hard. I'm tired of making others happy and getting nothing in return, thanks for your time.