If you're living with anybody who is struggling in any kind of intense way, hopefully you have already established when they were in a more rational state what you can do to best support them. If you haven't, then you support them in the best way you can, while also making sure that you're taking care of yourself. If you're not taking care of yourself, or you're trying to rescue somebody, it's going to be disastrous for everyone involved. The best thing you can do is be supportive, as best you can, within your own limitations and make sure you're taking care of yourself. Reach out to whatever support is needed to help that person if your limits have been reached.