First of all, happy birthday. I know it may not seem very happy right now, but it is still your day to celebrate. Don't let your H and his antics dictate what you do today.
I understand the done feeling. Only you can decide how much you can take and what is best for you and your girls. Do what is best for YOU!
Even if he leaves, maybe still try your best at some DB principles. The one I'm thinking of is Act, Don't React. You need to try not to act on pure emotion, even though its tough. I'm sure your H is going to continue to pull some sh!t. Be prepared. I like to think of different scenarios of things H might do or say, and how I should respond. This way I'm not caught off guard.
As for your BIL, I don't know if he was always a D-bag or not. In his defense, you KNOW that your H has most likely been telling him lies to look like the bad guy. He has too. He certainly can't tell his family the truth!
And why wouldn't your BIL not believe your H? They are brothers after all. We do tend to want to believe the best about our family. But, as someone once posted on here, reality always comes knocking. I believe this to be true. I think lies catch up with a person eventually, no matter how good they think the lies are.
Good luck and stay strong. You can do this! Thinking of you today and sending positive vibes your way
Bomb January 2012 - doesn't feel the same about me
~ "There is nothing love cannot face; there is no limit to its faith, hope, and endurance."