Yeah, even when you know, in your head, that it's the only sane thing to do, it's still very hard, sad, and just plain painful.
OTOH, you can take some comfort in knowing that you split up with a minimum of rancor. You each treated the other decently--especially as these kinds of situations go. You didn't shed unnecessary blood. Those are truly things to be grateful for--both of you.
And when/if she does decide to do the work to get sober, she won't have to deal with a mountain of resentments over the way things went. And you, yourself, won't have the huge resentments that come with a really UGLY breakup.
Be good to yourself over the next few weeks. It takes some time to feel less sad/bitter about how things turned out.
Hugs from me,