I would be able to keep my mouth shut - but screw it with respect to keeping everyone happy. 

But it's not your responsibility to keep everyone happy. Bless you, how could you?

Your job is to try to be a loving wife and support your spouse in their parenting efforts. Period. Dot. 

He needs to keep hos(intentional typo) kids happy. If the kids come to me to be entertained I give them chores and make them do homework and clean up after themselves, maybe do the bathroom. Not my job to make them happy.

If it gets too much I go out grocery shoppimg or with my single friends if I'm mad.

I have thought before how great things were going then whammo, hit smack in the face with a bunch of crap when I least expected it. You are right, it does create sadness. Sometimes I wonder if we all suffer from PTSD. My dh has a completely psycho bm and 1 sd who is identical to her. I used to be open and positive, now i have built a wall to protect myself from some of it and I hate that wall that i built, but what choice did i have. It does change you. Ive done some small stuff like going to a painting class here and there to get away from the crush of it and slowly start to rebuild my confidence that was completely destroyed. It's a looongg road ahead though. ugh.