Closure sometimes means different things to different people. And, unfortunately, sometimes there is no closure, no answer, no explanation.
That said, will it get better? Absolutely. Right now you are holding onto what's left -- the memories, the pain, the unanswered questions, etc. That's natural. You need to focus on yourself, detach and not enable -- the discussions, the conversations, the involvement, and so on. It takes two people to dance and you shouldn't be dancing with this person. This is hard to understand and even harder to do because you "are in it" right now. You are still vacillating and rationalizing in your head.
If you focus on yourself -- detach, don't enable, etc. -- then you will be able to let this go in a healthy way and you'll get past it. Go to meetings. Sometimes a spike in meetings helps. How many meetings are you going to a week? Do you have a sponsor? Make some calls. It will work.
Remember what the steward/stewardess/video says at the beginning of every single flight . . . if there is a drop in cabin pressure and the oxygen masks drop down from the ceiling . . . put the mask on yourself first, before you try to help the other person.
Stay strong. Focus on yourself.