I am not asking about motivating the spouse. But your feeling when you at an event or in public as a known fitness professional and people see you with your spouse who is very unfit.
It’s about you, not your spouse. They are free to make their own choices and live the way they feel is best for them and all you can do is set the example and hope they might follow. My wife likes to work out and stay fit, but even if she didn’t it would be ok with me.
Fortunately, my husband is in great shape himself. But ultimately, it is not the shape I married but the person. I have witnessed it with other couples, though, that with the ‘shape shift’ there came a ‘mind shift’ which put a strain on the relationship.