This is a tough nut to crack, and doctors are faced with moral and legal limits when making the decision to back a disability claim. The ultimate decision is not made by your own doctor, but by his recommendation, and verification by a goevernment employee. The legal course to permanent disability approval can be long, tortuous and expensive... note the number of lawyers who specialize in this.
My daughter-in-law was, until a few months ago, a lawyer working in Chicago, and responsible for governemnt disability expenditures for the midwest region. She probably saw more heartbreak and fraud than we would see in a thousand lifetimes. The road to approval can be very long, but, as mentioned above in this thread... once approved, would normally be retroactive.
That said, the hardest battle to fight is depression, and when there are two persons involved, the time needed for adjustment and acceptance is a difficult period. Living in senior communities for 25 years we have seen uncountable situations where there variances in the health of partners has been a life altering fact, but only in a very few cases... maybe five out of hundreds has the problem been insurmountable. The best outcomes are in situations where both partners make the extra effort to avoid cabin fever, by forcing socialization with others. Not only does this tend to take the stress off the healthier partner, but can build new relationships with others in the social group, for the less healthy partner.
It's hard to explain this, but we see it all the time. The stay at homes are always the ones who don't seem to adjust. It's a special effort, and finding the right group can make a world of difference.