Wow!...Good question. I would think some might hold on to a toxic relationship for fear of what emotional pain awaits them. I realized recently after some self reflection that I held on as much for me as I thought I held on for him and our marriage. I was afraid of being alone...I didn't want to be alone so at the time I allowed myself to suffer rather than journey on a quest for peace and self discovery.
When I finally filed for a divorce and he moved out of the house I healed in stages. He certainly gave me a good head start though because he basically sank further into his drug abuse. It just solidified my decision.
I could go on and on about my story but really everyone gets through it in their own way. I didn't just rip the bandaid off. I'm just not that type of person. The honest truth is..it just takes time. I don't think closing the doors on your emotions is the way to go because eventually everything comes back to bite you in the arse if not properly dealt with. Deal with what you are feeling, as painful as it might be, get past it and then move on. I don't mean to make it sound so simple b/c it isn't but it's possible. It does help to always remember the reason why you reached the end of your rope...why you finally chose to leave. Coming here and reading posts about people still going through what I was going through is a constant reminder of why I don't want to go backwards. I have many "Ahhhh....that's why" moments.
Take time for yourself. Remember all those times you used to rush home only to land in chaos and drama. All those times you holed yourself up at home because you didn't want him to run out and get high for just one day. All of those "going nowhere fast" arguments. All those times spent worrying and agonizing over where he is. Now....take a nice leisurly walk or drive home from work knowing that you are going home to peace and quiet and where he is really is none of your concern now. Enjoy a day out with friends and know that you can actually let loose and relax instead of wondering where he is and what he's doing at that very moment the whole time you are out. It's All So Very Exhausting! Revel in knowing that things never have to be the same again. You now control your time and what you do with it again.