It sounds like he took a lot longer to figure out where he belonged than you did. I don't know why he chose to turn on you when he did, but he seems genuinely sorry for having done it. But... if you ask him not to come near you, he'll probably do as you ask. You really don't have to accept his apology if you don't want to.

...but you'll have to find a firebending teacher eventually. If you don't want it to be him, I could teach you.