He has your back, even if you wake up one morning wanting to become an astronaut. He'll be supportive of your career and your life decisions from the big things to the little things. If you want to shave your head to donate your hair to charity then he should be being buying you wooly hats because it's going to get cold. As long as he treats you like a teammate then you don't need to worry about him always competing with you for first place, or leaving you before you've even finished the race together.