IcyHot

My partner and i have been in an awesome healthy relationship for over a year and a half now but one thing is frustrating. I am 20 and can hold an erection from sunset to sunrise, but sometimes i cannot cum no matter what we do. I have recieved oral sex for over an hour and not cum. We have sex for over 2 hours most times because i cannot cum and it feels great for her. I have the feeling of cumming several times but as it about to happen it does not happen. I have gone without any sexual contact for a month and after few weeks i thought i would pop at the slightest touch of her but i took me over 2 hours of sex to finally cum. My girlfriend comes during oral sex which i am more than happy to perform and cums during sex very often and she feels very selfish when she wants something compared to me wanting it 24/7 but only cumming every third time we have oral or sex. Are there any tips for me? Are there certain positions for male pleasure? Are there exercises i could do : ) ? Should we extend foreplay? We want to get it solved so we can be more equal in bed. Thanx in advance any and all suggestions would be so helpful!!!