The reason your age matters is because when you are young, as you obviously are, these things are often looked at from a different perspective.
In my AA home group, and MOST of the other ones that I have attended, I would say the average age is about fifty.
Are you willing to spend the next twenty years dealing with active addiction? Relapse after relapse?
You say that you won't tolerate it, but you already have. And you know what, the next time will happen, and you'll tell yourself, this time he got it. He really seems remorseful this time. He's hit bottom. And again and again.
It seems you just want people to tell you what you want to hear. You ASK for advice, but then argue against it.
I'm not trying to convince you of anything, but it seems your view of what you are facing is unrealistic.
I ask why you don't want better things for yourself because most people at a young age will run from almost certain disaster, yet you seem to believe in a very small chance of a good resolution. As you say, giving your addict boyfriend another chance.
I know there are a great many people here who started out much like yourself, believing that they would never be dragged down by an addict, yet here they are.
You are already here, despite your rosy predictions. Again, is this what you want out of a relationship? You say it hasn't interfered with your goals, is being with an addict one of your goals? If not, I'd say it already is.
In either case, I wish you all the luck in the world. I hope that I am wrong about this guy.