I disagree with the idea that you should let your sister know you are going to withdraw from the relationship. Just do it. You don't have to make an announcement. Why should you treat this as some kind of commitment? It is not necessary to predict what will seem right to you 6 months from now. I would say: let go of the relationship and then take it one day at a time. You don't owe your sister any explanation of anything. Let her figure it out as best she can. Avoid the trap of telling yourself or your sister: "Here's what I am going to do for the next ten years." Avoid getting into a debate with your sister. She is going to defend to the death that her behavior is fine. It's not. But she is the way she needs to be. If she misses you, after you detach from her, she may make overtures to close the gap. Or not. I doubt she is capable of being different from how she is.