My partner - John - is on several types of medication, I am not really sure what they are. I have only been with him for four months. Therapy is apparently 'not an option', I have largely left himself to himself to work out how to best handle things - or at least, that was my intent, until recently. Our planned engagement faltered when I realised I had no capabilities of coping with his distinct lapses in self-esteem, etc. It is very unstable at the moment. We are trying to work out how to bring him down from a 'paranoia attack' (I suppose you would call it) more naturally but my attempts so far have been largely unsuccessful.
Hopefully, things will begin to look better.
A book which I am reading right now is called "The Selfish Pig's Guide to Caring" by Hugh Marriott, a gift from a friend; though it is mostly geared towards physical disability, it has been quite helpful with handling personal guilt, etc, and fairly stopped me from just walking away. I haven't had the chance to read it all yet, but I would recommend it.