If maintaining an erection is a problem, or if sex feels dull, try taking supplements daily, which I have tried and found very helpful: zinc 30mg, choline/inositol 250mg each, flaxseed 1tbsp oil. The effects of the first two are immediate, flaxseed takes 2 weeks to start working but the effects are astonishing. If you are person who eats a bad diet, ie lots of unbalanced oils and fats, then fish oil may work better. I also recommend trying one of the following at a time: gingko (240mg extract) or scullcap (1200mg) or ashwaghanda (10g powder) or both of yellow dock (1000mg) and red clover (1000mg) . In my personal experience, the yellow dock works the best, and like flaxseed takes 1-2 weeks before you see the results - the results are that you will have a ridiculously engorged bonor, your girlfriend will feel the difference as well. And drinking lots of water and getting proper amounts of sleep, and not being stressed are probably more important that any of the supplements you can take.
I gave the above recommendation because you said masturbation also too long. Sex isn't all its lived up to be and I also gave up after an hour of having sex with my girlfriend. The condom is a killer - if you are using one, get lots of lube, make sure lube is fresh (goes bad easily) and get a thinner condom with bumps (like sherlon studded from condomdepot). Use lube, its a godsend. Try different positions. Have sex while you are kneeling, and have her sleeping sideways, fetal-position-like. Let me know what works and doesn't, i'd be glad to coach you through some of it.
