Did you ever work really hard on some project? After it's done, you may just want to relax and tend to the other areas of your life.
I don't know you and I don't know this guy's motivations. A lot of guys see the "intimacy" as the finish-line in a race. They're pushing and pushing towards the finish line and it's an effort. They take time from their lives to date you. They behave in a way that is different from their true selves to charm you. They spend their money on you. And all to reach that finish line. Maybe not just for that. But it's the reason they're spending time with somebody who is unlike them. Somebody who likes chick-flicks and wine instead of sports and beer. The bottom line is sex. After a hard-run race, once you finally cross the finish line, sometimes you just want to take a break from running the race. Some guys may also see the race as a challenge won and move on to the next challenge. Other guys come back.
Is this JW related? Because that could add a whole new set of complications. A JW may be driven by his hormones, but afterwards might feel guilty about what he's done. Which might lead him not to call.
How long was the relationship before this?
A number of things could be going on. 3 days does sound like a while. Especially if this was your first time together.