Jeez, that's a lot.
Good for him. Junk is the toughest habit to kick, so your absolutely right about the low success rate of cold turkey. Even after he kicks it watch and make sure he doesn't replace it with another substance, usually alcohol. I've had a couple friends who started as junkies and became alcoholics, it's tough to see.
Honestly, I don't know what to say about sticking by him. All I can say is for those two years, he was looking out for himself and feeding his habit behind your back, so if you decided you need to do what's best for you and leave, no one would judge you.
If your interested, you may want to read
Junky to gain some perspective. It's a semi-autobiographical account of Burroughs's habit from the late 40's through the 50's.
Good luck!