I really feel for your situation. In my experience, the behavior of adult children can be frightening hurtful. I am so sorry you are having such pain right now.

My daughter is 33 years old, by societal standards, she is successful in her life and is married to a responsible, caring man. I have always - always - put her needs before anyone else in my life. She is consistently angry with me and very disrespectful (unless she wants something from me, such as me caring for her cats while she's on vacation). I have discussed with her the hurt I feel in vain. The only solution I can come up with at this point is that I have allowed her to use me to a point at which she takes me for granted. (Sadly, she is not the kind of person who appreciates love so much as she emotionally abuses the person giving that love.) Anyway, I feel forced to set limitations/boundaries with my daughter. Saying "no" is the only way I can see that will cause her to stop pushing limits with me and, in turn, stop the terrible hurt I feel from her behavior.