Phil:
I am not quite as comfortable about someone staying in a bad marriage. I have seen it happen. On occasion, the family can ride it out successfully. But that is the exception. More often, the home environment is bitter. The fights, while perhaps not violent, are destabilizing for the family. Sometimes, they play the game well enough that the neighbors don’t know. But the kids almost always do.
These kids later enter marriages, and get into trouble. They did not merit seeing parents resolve disagreements, and have no model to do this. They then repeat what comprised their environment for most of their formative years. Result: The short term looks positive, with the absence of the bitter wars that characterize so many divorces. The long term is not so rosy, with children entering their own marriages with baggage.
I concur completely with the hiding of mental illness being completely wrong and disgusting. It is serious, and prevalent. I am aware of rabbonim who counsel and advise to withhold such information. The results are major destruction. The Chofetz Chaim was bold in guiding shidduch information to be open and honest, and that phohibition of lashon horah was not relevant to these situations.