Oh,no, another university professor fooling around with a student....been there, done that.

Get an attorney. Find out where you stand if he leaves so you know what you might have to live on financially. With 3 young children you need to prepare for the worst while trying to save this relationship. Be PREPARED to file for temporary support to keep you and the kids with money to live on. You never know what will happen.....it might work out in the end but it might not. You can't count on anything right now so prepare for all eventualities.

You are working against a university environment that probably doesn't condone but doesn't think too seriously of a prof/student affair. It's so common as to almost be not worth much notice in universities, and the chances of administration doing anything is slim.