I have only dated one person in my life except for a 15 yr-old boy LONG ago....so no help there, sorry.
I would be honest with the teacher. If you are going to date, then you should be honest. You don't have to talk badly about W, I know you wouldn't do that anyway. But tell the truth, she basically walked away from the marriage/family and you don't know who she is anymore. Or whatever you are comfortable sharing with her. Do what you feel is right, but if I were dating you, I would want to know the situation....
