I don't understand; you can't be separated and/or get a divorce if he's still living there with you, whether he sleeps on the couch or not; you have to live separate and apart for at least a year. If you are going to get divorced, one of you has to go elsewhere.

I don't see any interesting reason to stay friends with this woman; she hasn't given you anything you wanted/needed for even longer than your husband, it sounds like?