I've managed to stay friends with most of the people that I knew before I ever used dope who also now use. It's a small group of people compared to the total number of junkies I've known, some of whom behaved really scummy. This group of friends numbers six including me. At one time or another we've all had problems with each other, and various people, including myself, have gotten out of touch, sometimes for more than a year. We've been using for eight years.
My experience using heroin has been atypical, I aco wider myself blessed in the secular sense of the word to be a functional junkie, going and finishing high school after dropping out due to cocaine use, going to and graduating with great marks from college, holding on to friendships with non-users, going to work, etc. No dicksizing attempted, I expect that I am still functiona mostly because of pure luck and chance, with my attempts at discipline contributing but only in a minor way. Non-exceptionalistic about my good fortune, because I can still lose everything, and statistically speaking the longer I go functional the more likely I am to fail to sustain any success and crash and burn.
The other folks in this group of my close junkie friends are also to one degree or another functional as I am at the moment, most quite functional indeed but one very un-functional. We haven't stolen from eachother, though we have had problems paying eachother back for money lent. But all in all as junkies that are also friends go, we get on very well and I consider myself to be lucky to have had such an unlikely and uncommon social interaction.
So I would say its very possible to be friends with another junkie and have both a true, non-addiction based friendship and to not backstab eachother or otherwise fight/scam. That said, it seems to be very unlikely to have the rare, exact combination of personalities and random chance events required to sustain such friendships, at least based on other peoples' experiences listed in this thread. So it is possible, but very unlikely, to have real junkies as real friends for a long length of time.