You are responsible for contributing to a marriage that was difficult.
She is 100% responsible for choosing to abort the marriage. This wasn't your choice, it was hers. Saying you are responsible would be like telling a woman she is responsible for being raped because she wore suggestive clothing. It is appalling to me.
I appreciate wanting to be accountable for your shortcomings, and putting your energy into what you can control. I agree with all of that. It doesn't do any good focusing on your STBX. So by all means put the focus on you and only you. But I'd also say put the focus on the present and only the present. Don't look into the future. Just focus on the here and now, and take care of business. Time will pass and the road will be revealed. Don't worry about where it leads, if you take the right steps it will go where you're supposed to be.
I agree with what GB said about being careful of embracing the title of being 'the addict that destroyed your marriage'. I'm ok with you following your bishop's or counselors guidance to a point, in a confidential setting. But it is tempting to take on more than our share of burden to appear fair, just, etc. But it is actually false humility. And it is a covert contract. It has the expectation that if you are unfair in her favor that she will recognize that, or that God will and will praise you for it. But you know perfectly well you didn't end the marriage. Any more than your W did by withdrawing sexually from you. God helps those that help themselves too. Own your mistakes, but don't try to outrighteous her. Your kids need you. Just let it all go, and do what you need to do today.
Me:38 XW:38 T:11 years M:8 years Kids: S14, D11, D7 BD/Move out day: 6/17/14, D final Dec 15