The age difference was probably the most relevant factor, that and your general innocence. The fact that he taught you is only a bizarre, fun-mirror aspect of the relationship. You were taken in by an older man. But he didn’t have to groom you. He could see in a glance you were ready. And he was only too delighted to jump in, calculating correctly that he was outside his statute of limitations, and you were fair game. People sniff each other out in an instant.
Years ago, when I was in my early 30s, I was sitting in a cafe in Austria with a french fellow a few years older and three women, one from Switzerland and two from France. In a borrowed car, I had driven up with them to visit him. We chatted away the afternoon and then headed back into town. Later, I asked him what he’d thought of the Swiss, noting her self-confidence. He said, “Même plus que ça. Elle regarde un homme de voir s’il baise bien ou non.” He was totally right. She and I were sleeping together, but pretending we weren’t. She was 17.