I stayed with mine because I loved him, I understood the addiction and that he wasn't 'trying' to hurt me. I understood that the way he acted was due to his addiction and I still knew the person he was underneath, and desperately wanted to get that back. I wasn't ready to give up on growing old together (denial possibly). I was also scared of making it on my own as a single working parent. Most of all because we had a family and I would of done anything to hold us together.
But in the end, after years and years of fighting it, history repeating itself, being given hope then having it taken away again, getting repeatedly physically sick from the emotional trauma of it all, developing my own MO addiction in an attempt to fill the intimacy void without being unfaithful, I realised there was absolutely nothing I could do, I decided I needed to finally save my strength for me instead of exhausting myself on him, I had nothing more to give, and I left. And I left in a very dramatic fashion as a giant f*ck you. It was liberating and one of the best things I ever did for my wellbeing. I haven't been ill once since. And funnily enough, he's now in recovery and trying to prove himself, but there is no real future for us now aside from raising our child, it's too late. I needed him to take it seriously when we lived together and not let it get this far, but it fell on deaf ears.
PA's - if she's threatening to leave, you wanna be taking that seriously. SO's - if you're threatening to leave and nothing's changing, the addiction has more of a pull on his soul than you do, it's time to go.