Once you work your way up to H, where is there left to go? Nowhere.
Over time, god forbid - you will notice that the shell which opiate fiends 'may' project, is as fragile as the deception that they engage themselves in, but of which they have become a captive. The question then becomes, will you let them make a slave of you? Cause ultimatly it's all about getting high - not friendship, not respect. Too many will learn the hard way that the truth was there all along. It seems you have had a taste of it and perhaps have distanced yourself. Learn to recognise the signs for what they are. Do not allow yourself to become a victim of your own self pity, which is what opiate addiction is.
Your friend? Try and help as best you can, but remain strong and slip not into temptation. I think you became angry that he didn't share after you had shared with him all those times and yet he was doing you a favour! Maybe he even did that conciously because he cared about you too much! He may view his own life as fucked and seek to knumb himself in wonderland, but still retain a recognition that your life is 'ok' or 'better' or has 'potencial' which he probably does not see in himself. Maybe there is an opporunity for you both - to become life long friends who do have each others backs - who do respect and look out and show a sense of loyalty.
It is so indeed, people can be parasites - it be good to get a good filter going and seek good people who are genuine and can be trusted. For one can get to a place where one trusts no one at all - and that is the greatest sadness of all. Cynicsim beyond repair. Once you get there, H is probably a good option.
Seek not in others but seek to be fair and good and just. Ask not, want not.
I hope your friend makes it. He probably just needs a girl friend or something... and support. Bail not...its not over till its over. Ignore mediocrity and cultivate progress. Always carry some sense of detachment so you do not get too glued.