Your questions are important and obviously deeply-felt. I hesitate to offer answers to them because I don't think I'm particularly qualified as a philosopher to do that. But there are philosophers who hold themselves out as qualified; they're known as "philosophical practitioners," and you can find out more at this website. I don't know enough to say whether they're any good.
But a couple of responses do occur to me. You say that you're "responsible" for your family's happiness. If by that you mean "solely responsible" or "more responsible than any other member of the family," then I'd respectfully disagree. I don't see why one parent in the family has more responsibility for the collective happiness of the family than the other does. You also ask if it would be ethically OK for you to divorce if it hurts others. Unless you have reason to think that your divorce would be more hurtful to others than most divorces are, then really you're asking whether divorce, period, is ethically OK. I myself don't see anything ethically wrong with divorce as such.
But above all, I'd recommend talking about these questions with someone more professionally qualified to answer them than I am.