This story was painfully familiar. I had such a similar experience it was uncanny, and I have often felt bad about it since. The man in question obviously felt either hurt or affronted that I didn't want to see him again, and was really persistent in wanting to know why, wanting a second date, questioning my morals.
I questioned my morals a lot too, because I'd led him to believe I wanted to sleep with him, knowing full well that I really didn't. But the truth would have been even more unpalatable for him than my platitudes and him thinking I was a bad person. I slept with him because I stupidly, naively went to his house, in his car, and I was frightened that he might turn nasty if I didn't give him the evening he wanted. So when he started trying it on with me I got the sex over with as quickly as possible, made excuses for why I needed to get back but still tried to be bubbly, engaging and seem like I was enjoying myself so that he would drop me back into town. He would probably be mortified to hear that, and wouldn't understand it. But he had so much power, and whether he was aware of it or not, I was. And I did what I could to keep safe, all the while cursing myself for bowing to the pressure to continue a date in the spirit of giving him a chance.