I don't think you are cold hearted...i think that is like thinking self-care is selfish...It's not; it is healthy.
I think it is tough to know the right or wrong thing in so many situations dealing with our addicted kids. I found the best thing for me to do when I wasn't sure, was to examine my motives. Using your question about a text as an example, if I examined my own motives and decided I wanted not to respond because I thought it would "punish" my daughter and then she might feel guilted into a behavior change, I would have concerns about my course of action. But if I was not responding because I believed if I did I may be sucked back into the drama and that wouldn't be healthy for me, then I would feel better about my motives....If I wanted to respond just because I wanted her to know I was there and cared...sounds okay. If I was responding because I wanted to change her behavior...not so okay..
Do you have a sense of what feels right to you and what your motives are for that choice?