I think you may be onto something about your H being depressed. Until you know he's having an affair, don't assume he's having one. Be carefull though the failing buisness maybe be the catalyst that drives him into MLC. The OW is giving him something your not. My guess is he thinks she listens to him or makes him feel important. You can do the same thing. When he talks don't try to tell him what to do. Just listen, which is harder than you think.
The S who's 18 is he both of yours or his he from another M? When a child reaches adult hood, sometimes this can trigger an MLC. This is what happened to my sister.
