Why do I last longer in bed when I am drunk?

I think you are referring to the common occurrence of maintain an erection longer when you have alcohol in your system. Alcohol reduces inhibitions and causes a loss of control over some bodily and mental functions. If you are drunk, you may not experience sexual arosal in the same way that you would when you are sober. You also may not be able to feel the sensation as much when you are drunk due to alcohol’s numbing effect.

I think the reduction in physical and mental capacity both work together to reduce sensation during intercourse, allowing a male to “last longer”.