My husband and I did 26 years apiece, some of it apart, which we chose to do for better career advancement. I would never have asked him to give up command for me, and he would never have asked me to give it up - but that was us. There were also times when we mutually decided to take a sidestep, such as when I chose not to stay to 30 and potential promotion. Both of our 90+ year old mothers were in challenging elder care situations; it was too much for husband to handle solo. We shared the teamwork of being remote care-givers, and we agreed it was time for me to hang up my sword. There are many, many dual military career couples, and with good communications, shared goal-setting and values and a positive, adaptive approach (gee, sounds like classic advice for ANY marriage), two careers in uniform can be carved out. There are many variations, as you can see from the posts above - Reserve or Guard for one, or a mutual decision for one or both to get out. Dual military is a challenge that's been around since the mid-20th century. Used to be when women married or became pregnant, it was an automatic humanitarian discharge.... times have changed! That's also back when married women could not receive "with dependents" BAH even if they were married or had children, because the military and IRS did not consider them "heads of household." That took legal action in the 70's to fix! Your trivia for the day.
P.S. Coming up on 32 years of marriage.