OP, you sound lonely.
You can't change your DH's activity level. You can, perhaps naturally reduce portion size by cooking less.
It seems really important for you two to connect in ways that work right now. Maybe a weekly date night that is not hiking focused, etc.? With the empty nest stage approaching, time to invest in your relationship. Tell him that you miss sleeping in the same bed and encourage a sleep study and cpap if advised. Physical touch and cuddling is really important for health too. Find a new common hobby (not a sport), plan trips, maybe read and discuss books? Make plans for some of the date nights to be with other couples. Build your community as you are about to shift out of parenting mode. Maybe start here, both of you. Dorky but I know people it has really helped
https://5lovelanguages.com/
Try to be less black and white in thinking and less focused on the exercise you do and that he does not. I understand your concerns but there is a lot more to marriages and people than activity. To the extent it is driven by anxiety about health and the future, learn to manage that. We can only control ourselves. I found anxiety went up for me in midlife with hormone shifts and empty nesting looming.
It would be ironic if you divorce because you frayed the connection with lots of time spent separately, sleeping separately, etc. due to "love and concern for his longevity." Connect with your husband. Drop the rope of the power struggle, we cannot change or control other people. Go for strolls together, see movies, go to dinner and concerts, etc. Put deposits in the bank of shared, enjoyed, conflict free time. Love the husband you have.