I'm sorry you're feeling left behind, I'm sure it's gotta hurt since you were there for him.
While you were there for him I know all you wanted was for him to get healthy, perhaps this is his road to just that. Sometimes it just can't be about us even though we think we should be a part of the healing process we have to remember it's their addiction and they have to do it. You'll see things differently over time, perhaps you'll get back together perhaps not, but I'm sure you can take comfort in knowing you helped him on his path to a healthy life.