As someone with bipolar who was married for a really long time before the bipolar was diagnosed...there were times when I was not 'myself' and wanted out, or shut down, and in some cases said things I don't even remember but were hurtful and they weren't ME necessarily saying them, it was the episode coloring my thoughts. Depression lies to us and makes us lie to the people we love.
in so saying, if he is feeling very down and as if he's just not able to be with you because of his depression, then he probably really needs to see his dr.
not saying it will make him stay if he comes back up from the depression but it is worth a try.