Because he's goint through those dark adolescent years of being a troubled and rebellious teen. There's also the fact that he's a guy and like any other guy his age, he got some uncontrollable hormones, especially whenever the matter is related to Padme.
Okay, I was just rambling on for the fun of it. 😛 I don't really know if what I said even applies.
that's cause he got feelings for her, that's the entire point!
but you fail to mention those ten years before EpII where he probably was a good padawan
if he really didn't listen, why would he go and save OB1? he's like a father to him so of course, from time to time he doesn't listen and most of the time he does, just as with the emperor! ("I told you to wait on the commandship!"😉