Thanks thumb, but it's all relative. I don't think it's that SAD per say, but I know it could be a lot happier IYKWIM. 
MissClavel, how old were you when all this happened, I'm sensing young, a lot younger than we were.
We were 15 and 13. My Mum, who bless her, wasn't even 40, got (understandably) drunk one night. We came home from something to find her tipsy and a bottle of empty wine. Oh and she'd kicked through a canvas dad had bought, of a place in spain we'd never been, but OW and he had gone to for a weekend... (fair point)
Sis and I made a pact not to leave her on her own again, to keep an eye on her... 
She never knew till years later, she was hardly at risk of going off the rails, but to us, getting drunk for her was so odd, she only did it the once..
I am sorry for you MissClavel, it must have been horrendous and scary for you, especially if you were younger. But it's all proof in your mums case that what doesn't kill you makes you stronger! I am so glad to hear that she is a better person because of it. My mum is too.
Solost, this will be hard, it will be painful, you will feel all the emotions in the book and then some. The main thing is to keep talking, keep thinking straight, and stick with it.
Never lose sight of normal, we are here to help with that! You have a fantastic internal compass and I can guarantee that you will get through this and will come out the other side a much stronger and richer person.
H will lose all respect, will never regain it and will always be looked at as a traitor on some level. His loss, his doing.