If erection fails before ejaculation, how can I naturally keep an erection? -
Try to relax a lot more, more foreplay less penetration, leave penetration to nearly the last moment, but make sure you please you partner also, communicate your concerns with your partner, and I would suggest a penis ring, these are placed around the base of your penis and allow you to maintain an erection to ejaculation, there are lots on the market, and even ones that will tickle you partner too, and they do work, trust me.
Good luck and happy love making.
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Everything the lady above said and consider going to see a urologist, there may be a medical reason this is happening. Failure is no fun and if there is something you can fix now you will be happier for it.
Hmmm. Without more details it is hard to answer that one. Could be that your taking a long time to reach orgasm and thus are not able to sustain the erection long enough. Or it may be performance anxiety that is diminishing the both the erection and your performance. then again it coudl be that you are losing your mind (not literally though; more than it is wandering off to non-sexual venues and not staying with the current activity long enough to allow you to reach orgasm).
So, best suggestions
a) concentrate on what you are doing - do not let your mind wander off until the current activity is complete.
b) relax - do not worry about how good you are at sex or about having an orgasm or anything. Keep your mind focussed on the act not on the outcome or worry about how it will come out.
c) If it does seem to take forever to reach orgasm and that might be why yoru penis is giving up too early, experiment with different positions, forces and speed to see what will help decrease yoru time from arousal to orgasm. Remember bed is not the only place to have sex and man on woman is not th eonly way. Heck you can do it in an elevator standing on your heads if that helps. So be creative and enjoy.