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The liquid when the penis is erect is normal and is called pre-cum. Premature ejaculation
is due to excessive sensitivity. It needs training, to control and prolong your ejaculation. By practice you can achieve it. At the peak of stimulation divert your attention to something non-sexual, such as the pending work that you have to complete next day, and when the stimulus has subsided to a controllable level you can again engage yourself in sexual stimulus. By repeating this technique you can prolong the ejaculation until you really want it to happen.
Avoid handling your organ your self or by your partner at the peak of stimulus. Another method is asking your partner to hold tightly at the root of the penis when you feel you are about to cum.