Cut to the chase with him and set up an equitable visitation schedule with your mutual child and support if you have made a home for him all these years and not worked for pay outside the home. Get yourself ready to start supporting yourself if that is the case, and insist on support in the short term--and child support, including how your daughter will get higher education. Then let him run off with his lover. You might be inclined to fight for him; to put up with his lies and crud while he goes through his mid-life "I want young chicks now that I'm getting to be an old man" stuff--but keep in mind he might bright home sexually transmitted diseases, and the two of you are modeling life for your child: he's modeling cheating and you would be modeling….what?

You deserve better than he is shoveling out.