My BH was put on antidepressants in high school. He wasn't officially diagnosed with depression, and the antidepressants didn't help much so he stopped taking them. He is a little different than your BS, in that when he gets low, he completely withdraws into himself. He'll spend all his waking moments sitting in front of a computer, not speaking to me, barely eating, and staying up late into the night. This can last for days, weeks, or months.
You should stand up for yourself if you feel he is unjustly harsh. Even though he is your BS, and you are the WW, you don't deserve to be treated badly out of anger. Yes, he'll be angry, and you may think you deserve it, but if he's using his anger at the A to drag you through the mud every chance he gets, that's unhealthy.
Be there, let him know you support him and want to help him heal, but don't let him break you down for everything.