middle income people get about the same

Except that it is detached from the requirements of work, which is the guy's main source of stress. He could afford to make less money from his job because if he is getting 8k UBI annually he isn't going to be taxed an extra 8k annually directly out of his income. That's not how any of these proposals work. Certain programs get cut and certain spending redirected in order to fund UBI, and if there are tax increases they don't absolutely have to be on income tax. There are many ways to target taxation without biting directly into the life-line incomes of the middle class. Taxes on derivatives trading are one example.

There is also no evidence that his wife or other unemployed people are less likely to seek work under a modest UBI. It's actually the opposite, because people who were in no position to seek work before (homeless, no telephone, no training, etc) can suddenly afford the fundamentals that are required to bootstrap themselves. Very few UBI proposals are large enough to actually put someone near the poverty line without supplementation. The people who don't work under a UBI will be the same people who don't work today and they will have the same reasons. The poverty of a modest UBI is not significantly more attractive than the abject poverty of no income unless you are already incredibly desperate.

For the man in question, his wife's income will go up from nothing to whatever the UBI is, decreasing the stress he has from his job even further because his financial stability would be that much less tied to his job. Whether or not she works at that point would just be part of the negotiation with her husband about how they want to live their lives, like it is now. But it wouldn't be enough to fully support her without support from her husband and/or a job.