Well. you're right about that…but that's not what the law of the Church says.
Many, many annulments are given because the tribunal believes "suffering with [fill in the blank] is not what God wants for anyone", but, if each party was NOT mentally ill on the day of the wedding and if they both intended matrimony, and presuming the marriage was not illegal (age, consent, consummation, open to children), then, whether or not God wants the spouse of the now severely mentally ill [or whatever] person to suffer, that's what the law says he or she must do.
I’m not talking about Alzheimer’s or like that, I’m talking about mental illness that can be cured but the guy won’t go for help and they’re abusive. Some marriages have suffering but koy can be derived
If there’s abuse and denial with no hope, that’s what I’m talking about