John Walker's entire personality is (acts of) service. It applied to his time in the military, and it applies now that he's got his new team. He's still the person who jumps into the breach without a second thought to make sure the people he's responsible for are okay.
John doesn't think; he acts.
On the battlefield, he's a skilled tactician but often reckless when it comes to his own safety. He's the one who goes back in once he's gotten everyone else out.
John used to be like that in his marriage, too. Not thoughtless or rash but madly in love with Olivia and willing to show it at every opportunity, even if it made him look stupid.
He used to say "I love you" with actions rather than words, so when he stops acting, that's when Olivia starts to worry.
