There may be a wide variety of reasons why your daughter needs to take care of somebody less capable than she. From your heartfelt letter it isn’t possible to know what her motivation is. However, what is clear is your reaction and the need to take care of your daughter. This is the strongest feature to focus on.
Rather than trying to dissuade your daughter from her decision it is probably a better idea to shift to talking about your limitations with her boyfriend. Explain what you’re willing to do — and not do. Explain your difficulties in watching him treat her poorly and that you can’t accept it and won’t condone it. It’s important when you’re establishing your limits and boundaries to be clear that you love your daughter and have compassion for her, but for your own well-being, you’re not going to allow yourself to be silent or condone abusive or demeaning behavior from him.
It’s important to realize that your daughter may have to go through all of this with her boyfriend, but this doesn’t mean you have to ignore your feelings. She may not like what your limitations are, but at least you will have explained what they are.
If you have a therapist I would certainly begin talking about your feelings and reactions. If you don’t have a therapist you may want to find one to talk to as your friends are offering one perspective and it may be helpful to have another.
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral