It is a clear halacha that even if a parent or talmid chachom deteriorates he is still to be treated with kavod.
But what if it is a spouse who deveopd mental issues or dementia or diabetes or Parkinson's disease after decades of marriage. Is Divorce advisable?
What if this occurs after a couple become engaged or it is discovered that there was a serious health condition that they had concealed
In a normal situation where there is something intolerable so we say it is just tough accept this as your burden or get a divorce. Chazal say even if you don't like your wife's cooking it is grounds for divorce
I have only found a discussion regarding the husband taking care of a sick wife and this is because of the kesuba. What about the wife taking care of a senile husband?
"The husband must defray all medical expenses in case of his wife's illness. If she suffers from a disease which may be prolonged for many years, although legally he may pay her the amount fixed in her ketubah and give her a bill of divorce, such action is regarded as inhuman, and he is urged to provide all that is necessary for her cure (Ket. 51a; "Yad," l.c. xiv. 17; "Maggid Mishneh," ad loc.; Eben ha-'Ezer, 79; "Be'er Heṭeb," § 5; comp. "Pitḥe Teshubah" to 78, 1, concerning a case where sickness follows a fault of her own)."
Rambam (Marriage 14:17) When a woman becomes ill, her husband is obligated to provid medical treatment for her until she recovers. If the husband sees that her illness is prolonged, and he will be forced to spend much money treating her, he may tell her: "Here is the money due you by virtue of your ketubah. Either pay for your treatment from this money, or I will divorce you and pay you what is due you and abandon you." Although he is given this prerogative, it is not ethical to act in this manner. [As mentioned by the Maggid Mishneh and the Kessef Mishneh, there are authorities who maintain that there is an explicit prohibition preventing a husband from divorcing a wife who is too ill to care for herself. The later authorities, however, follow the Rambam's view. In the Ashkenazic community, there is a question if the Rambam's ruling applies in the present age, after the ban of Rabbenu Gershom, which prevents divorcing a woman against her will. (See the Chelkat Mechokek 79:3, which quotes an opinion that states that as long as the husband is prepared to meet all the financial obligations of the divorce, he has the prerogative to divorce a woman against her will, even when she is ill.)]
Kesubos (51a) IF SHE SUSTAINED AN INJURY IT IS HIS DUTY TO PROVIDE FOR HER MEDICAL TREATMENT, BUT IF HE SAID, HERE IS HER LETTER OF DIVORCE AND HER KETHUBAH, LET HER HEAL HERSELF, HE IS ALLOWED [TO ACT IN ACCORDANCE WITH HIS DESIRE].
Shulchan Aruch (EH 79:3) If a woman contracts a lasting disease, he is able to say to her that the ketuba can be assumed if she heals herself or the ketuba can be absolved and give her the ketuba , but this is not proper behavior because it is not derech eretz .