Unhappily married, and the love of my life is back in town... What should I do?

With or without the love of your life, you need to get out of that relationship that you are in now and soon. So why not kill two birds with one stone and get out and be with the love of your life too? But for sure get out of that abusive relationship so you are not injured or killed. I think it's quite possible for a future with the love of your life even if it's been 12 years. And if it don't work, at least you tried and you can both remain friends. But do dump that abusive so called husband you have. He is bad news.