A few ways for a guy to last longer is to focus on something besides how good his cock feels – how the sheets feel against his legs, the hum of the fridge, whatever. Another way is to really learn about your arousal – when you’re coming when masturbating, really think about how it felt before-hand, what lead you to the point-of-no-return, and then start practicing when masturbating. Bring yourself close to orgasm, and then ease off for a minute or so, while still doing some stimulation, but nothing too intense. Then do it again, and again. Keep doing this during masturbating, and you can bring it into partner-sex and last for much longer.