I have felt like you do now. I have a theory that what happens is that when terrible things happen we sometimes store them away for later so we can function. Then later, some time when you're otherwise feeling safe, they come back for dealing with.
It's clear to a blind man on a galloping horse that your husband and children love you. It's possible they don't have a frame of reference for what you're going through. My DH looked after me but he didn't understand what was happening so they can slip up and say things that make you feel worse - if this happens, just identify it with the part of your brain that can and try not to feel you have to keep thinking about it.
I don't think all depression is imbalance, chemical or otherwise, because of my theory about delaying dealing with horrors, which I think is a survival mechanism. You're not wrong or broken to be feeling like this when you're going through things that your mind put on one side until you felt safe enough to inspect them again. You were raped and you've carried guilt about it for years. Your birth mother sounds emotionally abusive. If you could go three weeks in deep depression without anyone noticing it sounds like our adoptive family haven't always been up to scratch either. This is legitimate trauma! It would break anyone into pieces! But you'll do this and experience all this pain and it will help you heal.
Try not to use our energy against yourself. ANYONE would be in your state, anyone. You are entitled to 'not cope' while you do this. Allow yourself to scream, cry, not go to work. If your child (God forbid) had something like this to deal with you would NEVER blame them for showing the pain- don't blame yourself.
I hope this is helpful rather than unhelpful. When I had my meltdown it took me a while to come to this way of thinking so I thought I'd pass on what thoughts I'd come to in the end.
You are loved. Your family love you, I believe God loves you, and in the way of agape-love from strangers, we love you :) this too will pass and you'll reflect on it as a hard time you went through, but something that's done.