The unanswered question here is: does your husband know what you did? If not, tell him. Tell him the whole story about how desperate and unsupported you were and how relieved you are to see him happier and doing better and how horrible you felt about doing it but you couldn't see any other options but divorce, but: tell him. If he doesn't know, I suspect a lot of what you're feeling guilty about is lying to him, not breaking the promise.

He might react poorly, though if he is worth anything as a husband, I expect he'll react better than you think, and it will let you clear the air and get stronger - and be a better united front against his parents going forward. (and if he does react unfixably badly, well, you'll get a lot more child support in the divorce now.)