Frequent masturbation lead to premature ejaculation.
There tips on how to increase sexual stamina:
2. It's very important to get adequate amounts of sleep (7-9 hours each night), because it will interfere with your sex drive. If you sleep little, you will get tired, lowers your libido. It's very important go to sleep before midnight, in this case you'll better feel in the morning.
3. Try to breath slowly and deeply during sex, relax your entire mind and body. Focus on keeping this slow relaxed rhythm. It can promote better self-control, therefore the orgasm will be easier to delay.
4. Women prefer slow and intense foreplay. So don't focus just on the actual sex, spend more time for foreplay. Don't hurry, stimulate her non-sexual areas first, and then her erogenous zones.
It doesn't affect your fertility. However, you might get used to obtain erections and orgasms only by masturbation and won't be able to achieve all this in a real situation. This happen to a number of men.