JJ2020: Obviously if it only happens after marriage, it’s a sign that Hashem wanted this to happen and for you to go through this. Yes I know mental illness can hit in the late twenties or thirties but it’s not the majority of cases.
Back to the majority, other posters are saying people KNEW their child has a mental illness yet did not seek treatment or diagnosis. THAT IS ABUSIVE. There is nothing else to say. Those parents are sick people.
A Rabbi is not a Navi, but I am looking for a boy with a close connection to a Rav, who would know about any issues. A proper and good Rav will pasken he must tell.