OP, please don't use words like "slapper". I typically get the first shag in within three dates, would you name call me like that?? Think about how misogynist that is for a sec... towards yourself and towards other women.
I know these threads LOVE to call the man names and talk about how men are "only after one thing" but honestly, that isn't really a thing. It's a lie women tell themselves to make themselves feel better and more secure as they move through the awkward, uncertain times of early dating.
Men are just taught to be more realistic than women when it comes to relationships. They treat dating the way it should be treated - as a test drive, for everything. Do we like the same things? Do we have easy conversations? Do we have fun together? Is there sexual chemistry? If a prospective partner falls on any of these hurdles, the average man will lose interest and cool off.
Whereas women are encouraged to look past any and all such hurdle-falls. You'll see it here all the time, with women desperately bargaining with God over some man who obviously isn't right for her.
In practice, this plays out as the man quietly and politely trying to move on from dating the woman - and the woman getting enraged/sad/etc asking herself what's wrong with her. Which is so unnecessary!!
In reality, if he has cooled off now, it's likely that he just didn't feel the chemistry he wished for during sex. Is that really so terrible? I have slept with absolutely lovely, gorgeous men with whom I was very disappointed to find I had no chemistry. I then cooled off and moved on. It was no-one's fault, it's disappointing sure, but I wasn't a monster for that.
This guy may have felt the same. Maybe it didn't feel right to him and he now isn't sure how to proceed, maybe he will want to have another go and see if it was just his nerves/etc in the way of chemistry, etc. I know it stings, but it's not about you being "a slapper"
it's just relationships and their mysterious ways.
He may have thought you absolutely lovely in every way, but having spent some time with you, realized that it just doesn't feel quite right. He may be really disappointed too. Or maybe you're both imagining things.
Have some compassion for yourself as well as a little for him - relationships are so awkward and we're all so vulnerable.