You were really young when you obtained your spider powers, too young.. you werent supposed to, but it happened. It was an anomaly, and Leo knew it, when he asked Shelldon to scan you and confirmed that you're the spiderperson of that universe, he was ready to take care of you, but you were just a kid.. Instead of that he took care of you, as your mentor, you're like his child. Years passed and you grew up, he never told you you're an anomaly, he just trained you, he's strict, but loving.