Nice that he's in rehab.. but wasn't it just a month or so ago he was all set to go run with the wolves? Yeah that "tear me apart put me together" stuff triggers me.. like rehab is a fix and he'll be better- any indications that he's aware that once he's out of rehab then the real work starts?
I'd propose your neutral position is an indication that you're NOT codie, and it feels weird because you're so used to being that way; stuffing till you explode, trying to love him out of it etc.. If feelings aren't facts then I'd also propose that lack of feelings is also not facts, if you'll pardon the grammar. If thats so then maybe what we're getting at is what you're thinking you're inclined to do as a response to him in rehab. Maybe nothing but get on with your own recovery, he'll get on with his or not and time will tell.
Sometimes the lack of conflict and simple peacefulness from one day to the next feels weird to me. Not being constantly triggered and frustrated and pissed off about something is kind of ...quiet. We had a speaker in my alanon homegroup who said her goal is to make sure nothing ever gets between her and her serenity, trying to make that my motto.