I recall that my ex-boyfriend seemed to take it personally when I was in a depressed mood. He would also try to cheer me up. I think the best things to remember are that depression doesn't have anything to do with you or the state of your relationship, and also that trying to cheer up a depressed person might actually make it worse. I would probably say try asking if there is anything you can do when your partner gets depressed, and if they want to be left alone, don't take it personally---this may be easier said than done, I think, because it's pretty hard not to take things personally. I don't know if I'm just telling you something you already know here, but these are the things that I vaguely recall having an effect on the relationship I had at the time. Unfortunately I don't know of any books, and I also don't know if an organization like NAMI could help you with that, as I haven't been in a relationship in quite some time. If anyone has any resources, I would be interested to know, as well.