So the situation is that I'm not the real father of my son. I call him my son since I love him very much, but he is my girlfriend's son from her previous relationship. 

I'm afraid though... He does listen to me.. for now. But I'm afraid that when the time comes, and he will be a teenager who rebels against everything, he will pop this line. 

I do think that I have a good relationship with him. He does love me, too. I can tell as much, but you know... Children are children, he will change his mind the first time I forbid him to smoke a cigar or whatever. 

So how should I handle this? This IS an ultimate defense. And a hurtful one too.