Nobody is totally happy all the time. People did not always think that the meaning of life was personal happiness and it seems the more this is thought of as a Utopia the more uncurable mental illness has occurred.
Nobody is totally responsible for the joy or misery of another.
We weren't talking about an abusive marriage, you added that into the mix like a Strawman. As far as I know DB hasn't beaten up VB, financially abused her or gaslighted her, the worst I heard was a possible affair. About half if marriages have had an affair happen, both parties in the marriage may be unaware.
We were talking about possible boredom, mental health issues like OCD or anorexia being challenging, lazyness, narcissism, FOMO, grass is greener, Post natal depression, possible physical health issues, rubbish job, charity work not getting you on the new years honour list, excessive travel, being too interested in materialism, rubbish economy, it can contribute to unhappiness and people can transfer that.