Hugs, Lilly,
Remember, they HAVE to blame others in their lives. They simply can't face owning responsibility for what has happened.
Someday, when/if (please, God) he does choose sobriety, he will speak of what you've done as the loving thing to do. And it is. And here's one other way to look at it--you are also sparing him the guilt he would otherwise have for even more pain he'd be putting you through if he were still under your roof.
I think it must be much tougher with kids than with partners. We are so conditioned to protecting them from everything.