Well, I disagree with most of the other posters. I think you are kind of an AH.

Did you react to him out of anger and that is why you turned him away?

It seems to me you both had a hellish childhood. He did the best he could. It did not turn out well for him. Maybe he turned to drugs because no one ever taught him how to cope otherwise.

I say he did not abandon you because he was not responsible for you. He left you because he aged out. Yes, he lost contact. You were left in a place that was rough, but it was not his choice. Although it was rough, it was safer than living on the streets.

I think you should talk with him. Maybe not at your place, but in a public place. At least listen to his side of the story. You have so much in common.

Helping him does not mean you inherit responsibility for him, nor does it mean he has to live with you.