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The prompt seems to come from a really rushed place. There’s “throughout… year” contrasted against “will take years” and then you have “want to get to know” contrasted against “threesome, perhaps foursome.” Like, it’s comedy. You’re not getting to know a person inside of two hours, unless it’s specifically in the most limited of biblical sense of knowing. Ask anyone in a long term relationship and it takes months to really know a person, and sexually? Even if you’re the most open of people it’s going to be nearly as long to learn how a person ‘ticks.’
I’m not really sure it’s the same as “exhaustion” sex, but one thing I loved is when my partner was into the aerobic exercise with me, and we’d both be slick with sweat and panting as we came back from the run/row/bike. Being almost unable to resist as entry is made? Ecstasy. Maybe the mere panting was enough, as it brought to mind the concept of being desperate for the other, or being heated and flushed was part of it, but something with the whole experience was mind-blowing.