Guys: can't come during sex?
Can you come when jacking off but not when having you're having sex? If so, you need to retrain your penis!
If you're having trouble actually coming when having sex with your girl but not when you're masturbating, it may be to do with the way you pleasure yourself.
If your masturbation technique is to squeeze the head of your penis hard or stroke it really hard and fast, your girl's vagina isn't ever going to match up to that. What you need to do is retrain your penis to get stimulated and turned on by the lightest touch and sensation.
Try not to masturbate for at least a week or as long as you can hold out – the longer the better – and then when you do, touch yourself gently and stroke yourself slowly, using only your fingertips. Don't give into temptation by gripping your dick hard and hammering away or you'll never get back on track.
Once you've tried this new masturbatory technique a few times, you should start feeling a difference during sex, aiming towards you coming when you make love to your girl.