There could be many reasons, men pull away for many reasons - fear of rejection; fear of success - if everything goes well and a break up - if he had experiences with bad breakups; he is busy. he is not that into you. also depends on you knowing each other. I had a case when I had known a girl since 7 yo - since school, and we started chatting and dated once when we were 24, I liked her a lot at school, and when we met, but I was too damn busy since 8 till 11pm, 7 days a week. I tried to call a few times but it was rare. I could have managed to meet her and call her more often if I would have been not scared of a failure, and not that busy. Relationships need time - and I didn't have time. She got married a year after we dated. I think that we have our separate routes in life. It was years ago. Hope it helps.
Or maybe he is just not that into you... like you thought the date was , amazing maybe he didn't think the same... people pretend to enjoy a date even if they are not cause they don't wanna hurt the other person's feelings
if they disappear completely like don't text you or keep in touch, then id say he's a player. but if he's genuinely busy and still cares about u, he would at least say hi to you everyday.