Again, this is just me, but I have found that being the one to take action, instead of simply reacting to someone else has granted me a powerful sense of freedom and ownership. It is OK to make a decision based on your needs alone and to act on that decision. It would be ok if you were 1 month into the relationship, and it's ok now.
For the Super Codie among us, it's so difficult to truthfully assert our needs without feeling like we're selfish. We automatically put others before ourselves because...we want to please, we want to "help", we want to be liked, to be nice, to be "a saint". So what if you're the one to end the marriage? It's no crime, it doesn't make you a quitter (seems to me you've given enough of your time and energy to this).
Try to remind yourself that if you don't take care of yourself, no one will. Your kids need a happy and healthy mama.
Perhaps it's time to close the door on this chapter of your life and let HP, instead of your AH, lead the way.