Nope, you are definitely not alone. I haven't been through nearly the trauma you are experiencing, and I'm so sorry you are having to deal with this.
I've only been with my heroin-addicted bf for just over a year, but I'm not leaving. We don't share the same things married people do (a home, kids, finances, etc.), so I can't say I share your experience. But I do share the sadness that comes from watching someone I love choose to hurt himself.
You have support here, and I hope all works out well for you and your little ones.