My MIL talked me into taking him back, trusting him again, more times than I can count. I did the dutiful obedient wife thing. Then after I kicked him out I called to let them know - She said "well, we always knew this day would come where we'd have to take care of him again"
She had hung me (and more importantly, her two innocent grandkids) out to dry all those years because SHE didn't want to "take him back over" Nice! In the meantime, we'd had tons of debt to our name, outbursts, chaos, mental and verbal abuse, etc. That's what my kids experienced because I didn't walk away from her (MIL) when she was talking.
Oddly, my FIL, who was seeing the massive amount of money that had been spent on drugs told me privately that if I filed for divorce I could protect my own assets/future earnings which would make my kids have a more stable financial life. He said divorce him on paper and take him back in a year or two if you still want. So that's how I pitched it to the ex - divorce on paper: if all goes well with you, we can get back together in 2 years.
Of course, it hasn't gone well for him. Relapses, rehab and drama. But that's no surprise considering his past. Luckily, I haven't had to pay for any of it since and the kids and I are having a fairly wonderful calm, happy life.
Just sharing my story...ignore if it doesn't apply to you.