You ALWAYS have a right to leave, whether he understands that or not. A few days, weeks, or months of good doesn't erase 12 years of bad. Sometimes, it's just too late. He's a grown man and is perfectly able to take care of himself. He doesn't need you there to hold his hand if he truly is serious about living a sober life. You deserve some peace and serenity in your own life and your children do, too. Don't allow him to make you feel guilty about something that you have no reason to feel guilty about.